$$reduce

Reduce an array with an initial value (identity) and a context transformer to a single value

Usage

{ 
  "$$reduce": /* Array of elements */,
  "to": /* Transformer(##accumulator,##current,##index) */,
  "identity": /* any */
}

"$$reduce(<to>,<identity>):{input}"

Returns

The reduced value (type of to or identity)

Arguments

Argument	Type	Values	Required / Default Value	Description
Primary	array		Yes	Array of elements
to	Transformer(##accumulator,##current,##index)		Yes	Transformer to apply on each element (with last accumulation) to get the next accumulation ##accumulator - Previously accumulated value ##current - Current element ##index - Current index
identity	any		Yes	Initial value to start the accumulation with

Examples

Input

Definition

Output

{
  "items": [
    {
      "id": "aaa",
      "amount": 10
    },
    {
      "id": "bbb",
      "amount": 20
    }
  ]
}

{
  "$$reduce": "$.items",
  "identity": 0,
  "to": {
    "$$math": [
      "##accumulator",
      "+",
      "##current.amount"
    ]
  }
}

30

Test

{
  "items": [
    {
      "id": "aaa",
      "amount": 10
    },
    {
      "id": "bbb",
      "amount": 20
    }
  ]
}

{
  "$$reduce": "aaa",
  "identity": "bbb",
  "to": "##current"
}

null

Test

{
  "items": [
    {
      "id": "aaa",
      "amount": 10
    },
    {
      "id": "bbb",
      "amount": 20
    }
  ]
}

"$$reduce('$$math(##accumulator,+,##current.amount)',0):$.items"

30

Test