mapGroups

mapGroups(array, keySelector, transform) → array · Array

Group array elements by key and transform each group. Returns an array of transformed results – ideal for reporting and aggregation. See Chapter 20.

array (required): input array to group
keySelector (required): lambda (item) -> key or string property name
transform (required): lambda receiving {key, value} group object

utlx

// Input: flat array of orders with region field
let sales = $input.orders
// [{region: "EU", amount: 100}, {region: "US", amount: 200}, ...]

{
  summary: mapGroups(sales, "region", (group) -> {
    region: group.key,
    count: count(group.value),
    total: sum(map(group.value, (o) -> o.amount))
  })
  // Output: [{region: "EU", count: 3, total: 450},
  //          {region: "US", count: 2, total: 380}]
}

bash

echo '[{"dept":"Eng","name":"Alice"},{"dept":"Eng","name":"Bob"},{"dept":"Sales","name":"Carol"}]' | utlx -e 'mapGroups($input, "dept", (g) -> {dept: g.key, headcount: count(g.value)})'
# [{"dept":"Eng","headcount":2},{"dept":"Sales","headcount":1}]

Difference from groupBy: groupBy returns an Object (keyed map for O(1) lookup); mapGroups returns an Array (for iteration/reporting).

mapGroups ​

mapGroups