Function

a!flatten( array )

Converts an array that contains other arrays into an array of single items.

Parameters

Returns

Any Type Array

Usage considerations

Understanding results

a!flatten() removes nesting from arrays, such as those created by looping functions. When passed a simple array, a!flatten() returns it unmodified.

Nulls are not removed from lists. Use reject() and isnull() to easily remove nulls from a flattened list.

a!flatten() always returns an array, so when passed a single item, a!flatten() returns an array containing that item.

When passed an empty or null array, a!flatten() returns an empty array.

If the array's type is Any Type, a!flatten() returns an array of the appropriate type.

Examples

Remove nesting from arrays

If you use a!forEach() to iterate over a list of items, it will return a nested list of arrays. For example:

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a!forEach(
  items: {1, 2, 3},
  expression: enumerate(fv!item)
)

Returns a three-item list consisting of {0}, {0, 1}, and {0, 1, 2}.

You can use a!flatten() to remove the nesting and return a single array. For example:

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a!flatten(
  a!forEach(
    items: {1, 2, 3},
    expression: enumerate(fv!item)
  )
)

Returns {0, 0, 1, 0, 1, 2}.

Only array nesting is removed when using a!flatten. Nested maps, dictionaries, and other data types retain their structure. For example, flattening an array containing a nested array of maps and a map with a nested map:

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a!flatten(
  {
    {
      a!map(id: 1), 
      a!map(id: 2),
    },
    a!map(
      id: 3,
      address: a!map(street: "Main Street", number: 101)
    )
  }
)

Returns a three-item list of maps. The nested map structure is unaffected:

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{
  a!map(id: 1),
  a!map(id: 2),
  a!map(id: 3, address: a!map(street: "Main Street", number: 101))
}

Retain data types

a!flatten() retains the data type of each array item.

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typename(
  typeof(
    a!flatten(
      a!map
        data: {1, 2, 3}
      ).data
    )
  )
)

Returns a list of integers.

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typename(
  typeof(
    a!flatten(
      a!map
        data: {1, 2, "a"}
      ).data
    )
  )
)

Returns list of variant types because the flattened array includes two numbers and a text string.

Feature compatibility