---
title: truncateTimeColumn() function
description: >
  `truncateTimeColumn()` truncates all input time values in the `_time` to a
  specified unit.
menu:
  flux_v0_ref:
    name: truncateTimeColumn
    parent: universe
    identifier: universe/truncateTimeColumn
weight: 101
flux/v0/tags: [transformations, date/time]
introduced: 0.37.0
---

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`truncateTimeColumn()` truncates all input time values in the `_time` to a
specified unit.

#### Truncate to weeks
When truncating a time value to the week (`1w`), weeks are determined using the
**Unix epoch (1970-01-01T00:00:00Z UTC)**. The Unix epoch was on a Thursday,
so all calculated weeks begin on Thursday.

##### Function type signature

```js
(<-tables: stream[{B with _time: C}], unit: duration, ?timeColumn: A) => stream[{B with _time: C, _time: time}] where C: Timeable
```

{{% caption %}}
For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
{{% /caption %}}

## Parameters

### unit
({{< req >}})
Unit of time to truncate to.

**Example units:**
- 1ns (nanosecond)
- 1us (microsecond)
- 1ms (millisecond)
- 1s (second)
- 1m (minute)
- 1h (hour)
- 1d (day)
- 1w (week)
- 1mo (month)
- 1y (year)

### timeColumn

Time column to truncate. Default is `_time`.

**Note:** Currently, assigning a custom value to this parameter will have
no effect.

### tables

Input data. Default is piped-forward data (`<-`).




## Examples

### Truncate all time values to the minute

```js
import "sampledata"

sampledata.int()
    |> truncateTimeColumn(unit: 1m)

```

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{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | 10      | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 17      | t1   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 13      | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:00Z | 10      | t1   |
| 2021-01-01T00:00:00Z | 7       | t1   |
| 2021-01-01T00:00:00Z | 17      | t1   |
| 2021-01-01T00:00:00Z | 15      | t1   |
| 2021-01-01T00:00:00Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:00Z | 4       | t2   |
| 2021-01-01T00:00:00Z | -3      | t2   |
| 2021-01-01T00:00:00Z | 19      | t2   |
| 2021-01-01T00:00:00Z | 13      | t2   |
| 2021-01-01T00:00:00Z | 1       | t2   |

{{% /expand %}}
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