yq/pkg/yqlib/doc/operators/headers/reduce.md

# Reduce

Reduce is a powerful way to process a collection of data into a new form.

```
<exp> as $<name> ireduce (<init>; <block>)
```

e.g.

```
.[] as $item ireduce (0; . + $item)
```

On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.

On the RHS there is `<init>`, the starting value of the accumulator and `<block>`, the expression that will update the accumulator for each element in the collection. Note that within the block expression, `.` will evaluate to the current value of the accumulator. 

## yq vs jq syntax
Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn't as sophisticated as `jq` and its only supports infix notation (e.g. a + b, where the operator is in the middle of the two parameters) - where as `jq` uses a mix of infix notation with _prefix_ notation (e.g. `reduce a b` is like writing `+ a b`).

To that end, the reduce operator is called `ireduce` for backwards compatibility if a `jq` like prefix version of `reduce` is ever added.
Update document generation script 2021-11-03 04:00:58 +00:00			`# Reduce`

Added reduce examples and doc 2021-02-15 05:38:53 +00:00			`Reduce is a powerful way to process a collection of data into a new form.`

Added context variable for reduce 2021-02-15 06:31:12 +00:00			```
			`<exp> as $<name> ireduce (<init>; <block>)`
			```

			`e.g.`

			```
			`.[] as $item ireduce (0; . + $item)`
			```

			On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.
Added reduce examples and doc 2021-02-15 05:38:53 +00:00
nicer reduce example 2021-02-15 07:23:50 +00:00			On the RHS there is `<init>`, the starting value of the accumulator and `<block>`, the expression that will update the accumulator for each element in the collection. Note that within the block expression, `.` will evaluate to the current value of the accumulator.
Added context variable for reduce 2021-02-15 06:31:12 +00:00
			`## yq vs jq syntax`
			Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn't as sophisticated as `jq` and its only supports infix notation (e.g. a + b, where the operator is in the middle of the two parameters) - where as `jq` uses a mix of infix notation with _prefix_ notation (e.g. `reduce a b` is like writing `+ a b`).
Added reduce examples and doc 2021-02-15 05:38:53 +00:00
Fix typo (#1222) 2022-05-24 08:18:27 +00:00			To that end, the reduce operator is called `ireduce` for backwards compatibility if a `jq` like prefix version of `reduce` is ever added.