refactor: apply suggestions from code review

Co-authored-by: Andrew Lamb <alamb@influxdata.com>

read_buffer/src/column/string.rs

@@ -209,8 +209,8 @@ impl StringEncoding {
         }
 
         // Rewrite all the encoded values into the new domain.
-        for id in keys.iter_mut() {
-            *id = *ordinal_mapping.get(id).unwrap();
+        for key in keys.iter_mut() {
+            *key = *ordinal_mapping.get(id).unwrap();
         }
 
         // now generate the values vector, which will contain the sorted set of

read_buffer/src/row_group.rs

@@ -2461,7 +2461,7 @@ west,4
         let tc = ColumnType::Time(Column::from(&[1_i64, 2, 3, 4, 5, 6][..]));
         columns.push(("time".to_string(), tc));
 
-        // Tag column that will be dictionary encoded when materilised
+        // Tag column that will be dictionary encoded when materialised
         let rc = ColumnType::Tag(Column::from(
             &["west", "west", "east", "west", "south", "north"][..],
         ));

read_buffer/src/value.rs

@@ -1351,6 +1351,7 @@ pub enum Values<'a> {
 
     // A dictionary mapping between a vector of dictionary integer keys and the
     // string values they refer to.
+    // NOTE the strings are always sorted
     Dictionary(Vec<u32>, Vec<Option<&'a str>>),
 
     // Scalar types