#summarizeWith

Applies an aggregate expression to each group’s key and results.

#summarizeWith(groups, @group: summary)

Category Grouping and aggregationValid in Property value

Parameters

Name	Type	Description
groups	path | array	Groups shaped like #groupBy output: { key, results }.
summary	lambda	Receives each group as @group with @group.key and @group.results.

Returns

array — An array of { key, value } objects.

Examples

Total per group

source.json

{
    "someArray": [
        { "groupingProperty": "A", "valueProperty": 1 },
        { "groupingProperty": "A", "valueProperty": 2 },
        { "groupingProperty": "B", "valueProperty": 3 }
    ]
}

transformer.json

{
    "summarizedArray": "#valueOf($.someArray)->#groupBy(@x: @x.groupingProperty)->#summarizeWith(@group: #sum(@group.results, @y: @y.valueProperty))"
}

output.json

{
    "summarizedArray": [ { "key": "A", "value": 3 }, { "key": "B", "value": 3 } ]
}

Try it in the playground →

Details

summarizeWith performs aggregation over grouped data. It’s easiest to understand starting from #groupBy.

Start with an array that could be grouped:

source.json

{
  "someArray": [
    { "groupingProperty": "A", "valueProperty": 1 },
    { "groupingProperty": "A", "valueProperty": 2 },
    { "groupingProperty": "B", "valueProperty": 3 }
  ]
}

A plain grouping keeps all of the original data:

{
  "groupedArray": "#groupBy($.someArray, @x: @x.groupingProperty)"
}

output.json

{
  "groupedArray": [
    {
      "key": "A",
      "results": [
        { "groupingProperty": "A", "valueProperty": 1 },
        { "groupingProperty": "A", "valueProperty": 2 }
      ]
    },
    {
      "key": "B",
      "results": [
        { "groupingProperty": "B", "valueProperty": 3 }
      ]
    }
  ]
}

That’s verbose. To get just the total of valueProperty per group, pipe the groups into summarizeWith. Its lambda receives each group as @group, with @group.key and @group.results:

{
  "summarizedArray": "#valueOf($.someArray)->#groupBy(@x: @x.groupingProperty)->#summarizeWith(@group: { 'name': @group.key + ' total', 'totalValue': #sum(@group.results, @y: @y.valueProperty) })"
}

Each output element keeps the group’s key, and the lambda’s result becomes its value:

output.json

{
  "summarizedArray": [
    { "key": "A", "value": { "name": "A total", "totalValue": 3 } },
    { "key": "B", "value": { "name": "B total", "totalValue": 3 } }
  ]
}

The summary doesn’t have to be an object. #summarizeWith(@group: #sum(@group.results)) on the same groups would produce { "key": "A", "value": 3 } and { "key": "B", "value": 3 }.

Without groupBy

summarizeWith doesn’t have to follow #groupBy. Any array of objects shaped like its output, with a key and a results array, works. #groupBy just does that work for you.

Related

#groupBy · #sum