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22 lines
1.1 KiB
Markdown
22 lines
1.1 KiB
Markdown
Reduce is a powerful way to process a collection of data into a new form.
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```
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<exp> as $<name> ireduce (<init>; <block>)
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```
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e.g.
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```
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.[] as $item ireduce (0; . + $item)
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```
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On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.
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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.
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## yq vs jq syntax
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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`).
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To that end, the reduce operator is called `ireduce` for backwards compatability if a `jq` like prefix version of `reduce` is ever added.
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