898 lines
19 KiB
Markdown
898 lines
19 KiB
Markdown
---
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title: EvalNode
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description: >
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EvalNode evaluates expressions on each data point it receives. A list of expressions may be provided and will be evaluated in the order they are given. The results of expressions are available to later expressions in the list.
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note: Auto generated by tickdoc
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menu:
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kapacitor_1_6_ref:
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name: EvalNode
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identifier: eval_node
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weight: 100
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parent: nodes
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---
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The `eval` node evaluates expressions on each data point it receives.
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A list of expressions may be provided and will be evaluated in the order they are given.
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The results of expressions are available to later expressions in the list.
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See the property [EvalNode.As](/kapacitor/v1.6/nodes/eval_node/#as) for details on how to reference the results.
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Example:
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```js
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stream
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|eval(lambda: "error_count" / "total_count")
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.as('error_percent')
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```
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The above example will add a new field `error_percent` to each
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data point with the result of `error_count / total_count` where
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`error_count` and `total_count` are existing fields on the data point.
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Available Statistics:
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* eval_errors: number of errors evaluating any expressions.
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### Constructor
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| Chaining Method | Description |
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|:---------|:---------|
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| **eval ( `expressions` `...ast.LambdaNode`)** | Create an eval node that will evaluate the given transformation function to each data point. A list of expressions may be provided and will be evaluated in the order they are given. The results are available to later expressions. |
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### Property Methods
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| Setters | Description |
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|:---|:---|
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| **[as](#as) ( `names` `...string`)** | List of names for each expression. The expressions are evaluated in order. The result of an expression may be referenced by later expressions via the name provided. |
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| **[keep](#keep) ( `fields` `...string`)** | If called the existing fields will be preserved in addition to the new fields being set. If not called then only new fields are preserved. (Tags are always preserved regardless how `keep` is used.) |
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| **[quiet](#quiet) ( )** | Suppress all error logging events from this node. |
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| **[tags](#tags) ( `names` `...string`)** | Convert the result of an expression into a tag. The result must be a string. Use the `string()` expression function to convert types. |
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### Chaining Methods
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[Alert](#alert),
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[Barrier](#barrier),
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[Bottom](#bottom),
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[ChangeDetect](#changedetect),
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[Combine](#combine),
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[Count](#count),
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[CumulativeSum](#cumulativesum),
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[Deadman](#deadman),
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[Default](#default),
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[Delete](#delete),
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[Derivative](#derivative),
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[Difference](#difference),
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[Distinct](#distinct),
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[Ec2Autoscale](#ec2autoscale),
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[Elapsed](#elapsed),
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[Eval](#eval),
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[First](#first),
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[Flatten](#flatten),
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[GroupBy](#groupby),
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[HoltWinters](#holtwinters),
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[HoltWintersWithFit](#holtwinterswithfit),
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[HttpOut](#httpout),
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[HttpPost](#httppost),
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[InfluxDBOut](#influxdbout),
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[Join](#join),
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[K8sAutoscale](#k8sautoscale),
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[KapacitorLoopback](#kapacitorloopback),
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[Last](#last),
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[Log](#log),
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[Max](#max),
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[Mean](#mean),
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[Median](#median),
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[Min](#min),
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[Mode](#mode),
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[MovingAverage](#movingaverage),
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[Percentile](#percentile),
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[Sample](#sample),
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[Shift](#shift),
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[Sideload](#sideload),
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[Spread](#spread),
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[StateCount](#statecount),
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[StateDuration](#stateduration),
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[Stats](#stats),
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[Stddev](#stddev),
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[Sum](#sum),
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[SwarmAutoscale](#swarmautoscale),
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[Top](#top),
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[Trickle](#trickle),
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[Union](#union),
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[Where](#where),
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[Window](#window)
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---
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## Properties
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Property methods modify state on the calling node.
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They do not add another node to the pipeline, and always return a reference to the calling node.
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Property methods are marked using the `.` operator.
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### As
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List of names for each expression.
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The expressions are evaluated in order. The result
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of an expression may be referenced by later expressions
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via the name provided.
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Example:
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```js
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stream
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|eval(lambda: "value" * "value", lambda: 1.0 / "value2")
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.as('value2', 'inv_value2')
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```
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The above example calculates two fields from the value and names them
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`value2` and `inv_value2` respectively.
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```js
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eval.as(names ...string)
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```
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### Keep
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If called the existing fields will be preserved in addition
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to the new fields being set.
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If not called then only new fields are preserved. (Tags are
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always preserved regardless how `keep` is used.)
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Optionally, intermediate values can be discarded
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by passing a list of field names to be kept.
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Only fields in the list will be retained, the rest will be discarded.
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If no list is given then all fields are retained.
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Example:
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```js
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stream
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|eval(lambda: "value" * "value", lambda: 1.0 / "value2")
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.as('value2', 'inv_value2')
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.keep('value', 'inv_value2')
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```
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In the above example the original field `value` is preserved.
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The new field `value2` is calculated and used in evaluating
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`inv_value2` but is discarded before the point is sent on to child nodes.
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The resulting point has only two fields: `value` and `inv_value2`.
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```js
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eval.keep(fields ...string)
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```
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### Quiet
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Suppress all error logging events from this node.
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```js
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eval.quiet()
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```
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### Tags
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Convert the result of an expression into a tag.
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The result must be a string.
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Use the `string()` expression function to convert types.
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Example:
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```js
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stream
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|eval(lambda: string(floor("value" / 10.0)))
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.as('value_bucket')
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.tags('value_bucket')
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```
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The above example calculates an expression from the field `value`, casts it as a string, and names it `value_bucket`.
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The `value_bucket` expression is then converted from a field on the point to a tag `value_bucket` on the point.
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Example:
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```js
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stream
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|eval(lambda: string(floor("value" / 10.0)))
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.as('value_bucket')
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.tags('value_bucket')
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.keep('value') // keep the original field `value` as well
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```
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The above example calculates an expression from the field `value`, casts it as a string, and names it `value_bucket`.
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The `value_bucket` expression is then converted from a field on the point to a tag `value_bucket` on the point.
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The `keep` property preserves the original field `value`.
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Tags are always kept since creating a tag implies you want to keep it.
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```js
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eval.tags(names ...string)
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```
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## Chaining Methods
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Chaining methods create a new node in the pipeline as a child of the calling node.
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They do not modify the calling node.
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Chaining methods are marked using the `|` operator.
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### Alert
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Create an alert node, which can trigger alerts.
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```js
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eval|alert()
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```
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Returns: [AlertNode](/kapacitor/v1.6/nodes/alert_node/)
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### Barrier
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Create a new Barrier node that emits a BarrierMessage periodically.
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One BarrierMessage will be emitted every period duration.
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```js
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eval|barrier()
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```
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Returns: [BarrierNode](/kapacitor/v1.6/nodes/barrier_node/)
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### Bottom
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Select the bottom `num` points for `field` and sort by any extra tags or fields.
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```js
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eval|bottom(num int64, field string, fieldsAndTags ...string)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### ChangeDetect
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Create a new node that only emits new points if different from the previous point.
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```js
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eval|changeDetect(field string)
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```
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Returns: [ChangeDetectNode](/kapacitor/v1.6/nodes/change_detect_node/)
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### Combine
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Combine this node with itself. The data is combined on timestamp.
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```js
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eval|combine(expressions ...ast.LambdaNode)
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```
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Returns: [CombineNode](/kapacitor/v1.6/nodes/combine_node/)
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### Count
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Count the number of points.
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```js
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eval|count(field string)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### CumulativeSum
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Compute a cumulative sum of each point that is received.
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A point is emitted for every point collected.
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```js
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eval|cumulativeSum(field string)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### Deadman
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Helper function for creating an alert on low throughput, a.k.a. deadman's switch.
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- Threshold: trigger alert if throughput drops below threshold in points/interval.
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- Interval: how often to check the throughput.
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- Expressions: optional list of expressions to also evaluate. Useful for time of day alerting.
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Example:
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```js
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var data = stream
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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data
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|deadman(100.0, 10s)
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//Do normal processing of data
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data...
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```
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The above is equivalent to this example:
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```js
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var data = stream
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|from()...
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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data
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|stats(10s)
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.align()
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|derivative('emitted')
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.unit(10s)
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.nonNegative()
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|alert()
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.id('node \'stream0\' in task \'{{ .TaskName }}\'')
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.message('{{ .ID }} is {{ if eq .Level "OK" }}alive{{ else }}dead{{ end }}: {{ index .Fields "emitted" | printf "%0.3f" }} points/10s.')
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.crit(lambda: "emitted" <= 100.0)
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//Do normal processing of data
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data...
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```
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The `id` and `message` alert properties can be configured globally via the 'deadman' configuration section.
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Since the [AlertNode](/kapacitor/v1.6/nodes/alert_node/) is the last piece it can be further modified as usual.
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Example:
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```js
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var data = stream
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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data
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|deadman(100.0, 10s)
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.slack()
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.channel('#dead_tasks')
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//Do normal processing of data
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data...
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```
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You can specify additional lambda expressions to further constrain when the deadman's switch is triggered.
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Example:
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```js
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var data = stream
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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// Only trigger the alert if the time of day is between 8am-5pm.
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data
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|deadman(100.0, 10s, lambda: hour("time") >= 8 AND hour("time") <= 17)
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//Do normal processing of data
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data...
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```
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```js
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eval|deadman(threshold float64, interval time.Duration, expr ...ast.LambdaNode)
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```
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Returns: [AlertNode](/kapacitor/v1.6/nodes/alert_node/)
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### Default
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Create a node that can set defaults for missing tags or fields.
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```js
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eval|default()
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```
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Returns: [DefaultNode](/kapacitor/v1.6/nodes/default_node/)
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### Delete
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Create a node that can delete tags or fields.
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```js
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eval|delete()
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```
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Returns: [DeleteNode](/kapacitor/v1.6/nodes/delete_node/)
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### Derivative
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Create a new node that computes the derivative of adjacent points.
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```js
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eval|derivative(field string)
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```
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Returns: [DerivativeNode](/kapacitor/v1.6/nodes/derivative_node/)
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### Difference
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Compute the difference between points independent of elapsed time.
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```js
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eval|difference(field string)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### Distinct
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Produce batch of only the distinct points.
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```js
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eval|distinct(field string)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### Ec2Autoscale
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Create a node that can trigger autoscale events for a ec2 autoscalegroup.
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```js
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eval|ec2Autoscale()
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```
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Returns: [Ec2AutoscaleNode](/kapacitor/v1.6/nodes/ec2_autoscale_node/)
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### Elapsed
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Compute the elapsed time between points.
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```js
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eval|elapsed(field string, unit time.Duration)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### Eval
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Create an eval node that will evaluate the given transformation function to each data point.
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A list of expressions may be provided and will be evaluated in the order they are given.
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The results are available to later expressions.
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```js
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eval|eval(expressions ...ast.LambdaNode)
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```
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Returns: [EvalNode](/kapacitor/v1.6/nodes/eval_node/)
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### First
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Select the first point.
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```js
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eval|first(field string)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### Flatten
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Flatten points with similar times into a single point.
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```js
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eval|flatten()
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```
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Returns: [FlattenNode](/kapacitor/v1.6/nodes/flatten_node/)
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### GroupBy
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Group the data by a set of tags.
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Can pass literal * to group by all dimensions.
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Example:
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```js
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|groupBy(*)
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```
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```js
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eval|groupBy(tag ...interface{})
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```
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Returns: [GroupByNode](/kapacitor/v1.6/nodes/group_by_node/)
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### HoltWinters
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Compute the Holt-Winters (/{{< latest "influxdb" "v1" >}}/query_language/functions/#holt-winters) forecast of a data set.
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```js
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eval|holtWinters(field string, h int64, m int64, interval time.Duration)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### HoltWintersWithFit
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Compute the Holt-Winters (/{{< latest "influxdb" "v1" >}}/query_language/functions/#holt-winters) forecast of a data set.
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This method also outputs all the points used to fit the data in addition to the forecasted data.
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```js
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eval|holtWintersWithFit(field string, h int64, m int64, interval time.Duration)
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```
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Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
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### HttpOut
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Create an HTTP output node that caches the most recent data it has received.
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The cached data is available at the given endpoint.
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The endpoint is the relative path from the API endpoint of the running task.
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For example, if the task endpoint is at `/kapacitor/v1/tasks/<task_id>` and endpoint is
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`top10`, then the data can be requested from `/kapacitor/v1/tasks/<task_id>/top10`.
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```js
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eval|httpOut(endpoint string)
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```
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Returns: [HTTPOutNode](/kapacitor/v1.6/nodes/http_out_node/)
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### HttpPost
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Creates an HTTP Post node that POSTS received data to the provided HTTP endpoint.
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HttpPost expects 0 or 1 arguments. If 0 arguments are provided, you must specify an
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endpoint property method.
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```js
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eval|httpPost(url ...string)
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```
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Returns: [HTTPPostNode](/kapacitor/v1.6/nodes/http_post_node/)
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### InfluxDBOut
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Create an influxdb output node that will store the incoming data into InfluxDB.
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```js
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eval|influxDBOut()
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```
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Returns: [InfluxDBOutNode](/kapacitor/v1.6/nodes/influx_d_b_out_node/)
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### Join
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Join this node with other nodes. The data is joined on timestamp.
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```js
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eval|join(others ...Node)
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```
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Returns: [JoinNode](/kapacitor/v1.6/nodes/join_node/)
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### K8sAutoscale
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Create a node that can trigger autoscale events for a kubernetes cluster.
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```js
|
|
eval|k8sAutoscale()
|
|
```
|
|
|
|
Returns: [K8sAutoscaleNode](/kapacitor/v1.6/nodes/k8s_autoscale_node/)
|
|
|
|
### KapacitorLoopback
|
|
|
|
Create an kapacitor loopback node that will send data back into Kapacitor as a stream.
|
|
|
|
|
|
```js
|
|
eval|kapacitorLoopback()
|
|
```
|
|
|
|
Returns: [KapacitorLoopbackNode](/kapacitor/v1.6/nodes/kapacitor_loopback_node/)
|
|
|
|
### Last
|
|
|
|
Select the last point.
|
|
|
|
|
|
```js
|
|
eval|last(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Log
|
|
|
|
Create a node that logs all data it receives.
|
|
|
|
|
|
```js
|
|
eval|log()
|
|
```
|
|
|
|
Returns: [LogNode](/kapacitor/v1.6/nodes/log_node/)
|
|
|
|
### Max
|
|
|
|
Select the maximum point.
|
|
|
|
|
|
```js
|
|
eval|max(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Mean
|
|
|
|
Compute the mean of the data.
|
|
|
|
|
|
```js
|
|
eval|mean(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Median
|
|
|
|
Compute the median of the data.
|
|
|
|
> **Note:** This method is not a selector.
|
|
If you want the median point, use `.percentile(field, 50.0)`.
|
|
|
|
|
|
```js
|
|
eval|median(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Min
|
|
|
|
Select the minimum point.
|
|
|
|
|
|
```js
|
|
eval|min(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Mode
|
|
|
|
Compute the mode of the data.
|
|
|
|
|
|
```js
|
|
eval|mode(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### MovingAverage
|
|
|
|
Compute a moving average of the last window points.
|
|
No points are emitted until the window is full.
|
|
|
|
|
|
```js
|
|
eval|movingAverage(field string, window int64)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Percentile
|
|
|
|
Select a point at the given percentile. This is a selector function, no interpolation between points is performed.
|
|
|
|
|
|
```js
|
|
eval|percentile(field string, percentile float64)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Sample
|
|
|
|
Create a new node that samples the incoming points or batches.
|
|
|
|
One point will be emitted every count or duration specified.
|
|
|
|
|
|
```js
|
|
eval|sample(rate interface{})
|
|
```
|
|
|
|
Returns: [SampleNode](/kapacitor/v1.6/nodes/sample_node/)
|
|
|
|
### Shift
|
|
|
|
Create a new node that shifts the incoming points or batches in time.
|
|
|
|
|
|
```js
|
|
eval|shift(shift time.Duration)
|
|
```
|
|
|
|
Returns: [ShiftNode](/kapacitor/v1.6/nodes/shift_node/)
|
|
|
|
### Sideload
|
|
|
|
Create a node that can load data from external sources.
|
|
|
|
|
|
```js
|
|
eval|sideload()
|
|
```
|
|
|
|
Returns: [SideloadNode](/kapacitor/v1.6/nodes/sideload_node/)
|
|
|
|
### Spread
|
|
|
|
Compute the difference between `min` and `max` points.
|
|
|
|
|
|
```js
|
|
eval|spread(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### StateCount
|
|
|
|
Create a node that tracks number of consecutive points in a given state.
|
|
|
|
|
|
```js
|
|
eval|stateCount(expression ast.LambdaNode)
|
|
```
|
|
|
|
Returns: [StateCountNode](/kapacitor/v1.6/nodes/state_count_node/)
|
|
|
|
### StateDuration
|
|
|
|
Create a node that tracks duration in a given state.
|
|
|
|
|
|
```js
|
|
eval|stateDuration(expression ast.LambdaNode)
|
|
```
|
|
|
|
Returns: [StateDurationNode](/kapacitor/v1.6/nodes/state_duration_node/)
|
|
|
|
### Stats
|
|
|
|
Create a new stream of data that contains the internal statistics of the node.
|
|
The interval represents how often to emit the statistics based on real time.
|
|
This means the interval time is independent of the times of the data points the source node is receiving.
|
|
|
|
|
|
```js
|
|
eval|stats(interval time.Duration)
|
|
```
|
|
|
|
Returns: [StatsNode](/kapacitor/v1.6/nodes/stats_node/)
|
|
|
|
### Stddev
|
|
|
|
Compute the standard deviation.
|
|
|
|
|
|
```js
|
|
eval|stddev(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Sum
|
|
|
|
Compute the sum of all values.
|
|
|
|
|
|
```js
|
|
eval|sum(field string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### SwarmAutoscale
|
|
|
|
Create a node that can trigger autoscale events for a Docker swarm cluster.
|
|
|
|
|
|
```js
|
|
eval|swarmAutoscale()
|
|
```
|
|
|
|
Returns: [SwarmAutoscaleNode](/kapacitor/v1.6/nodes/swarm_autoscale_node/)
|
|
|
|
### Top
|
|
|
|
Select the top `num` points for `field` and sort by any extra tags or fields.
|
|
|
|
|
|
```js
|
|
eval|top(num int64, field string, fieldsAndTags ...string)
|
|
```
|
|
|
|
Returns: [InfluxQLNode](/kapacitor/v1.6/nodes/influx_q_l_node/)
|
|
|
|
### Trickle
|
|
|
|
Create a new node that converts batch data to stream data.
|
|
|
|
```js
|
|
eval|trickle()
|
|
```
|
|
|
|
Returns: [TrickleNode](/kapacitor/v1.6/nodes/trickle_node/)
|
|
|
|
### Union
|
|
|
|
Perform the union of this node and all other given nodes.
|
|
|
|
|
|
```js
|
|
eval|union(node ...Node)
|
|
```
|
|
|
|
Returns: [UnionNode](/kapacitor/v1.6/nodes/union_node/)
|
|
|
|
### Where
|
|
|
|
Create a new node that filters the data stream by a given expression.
|
|
|
|
|
|
```js
|
|
eval|where(expression ast.LambdaNode)
|
|
```
|
|
|
|
Returns: [WhereNode](/kapacitor/v1.6/nodes/where_node/)
|
|
|
|
### Window
|
|
|
|
Create a new node that windows the stream by time.
|
|
|
|
NOTE: Window can only be applied to stream edges.
|
|
|
|
|
|
```js
|
|
eval|window()
|
|
```
|
|
|
|
Returns: [WindowNode](/kapacitor/v1.6/nodes/window_node/)
|