yq/pkg/yqlib/doc/Reduce.md

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

## 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, 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 compatability if a prefix version of `reduce` is ever added.


## Sum numbers
Given a sample.yml file of:
```yaml
- 10
- 2
- 5
- 3
```
then
```bash
yq eval '.[] as $item ireduce (0; . + $item)' sample.yml
```
will output
```yaml
20
```

## Convert an array to an object
Given a sample.yml file of:
```yaml
- name: Cathy
  has: apples
- name: Bob
  has: bananas
```
then
```bash
yq eval '.[] as $item ireduce ({}; .[$item | .name] = ($item | .has) )' sample.yml
```
will output
```yaml
Cathy: apples
Bob: bananas
```