a!forEach() Function

Function

a!forEach( items, expression )

Evaluates an expression for each item in a list and returns a new array of the results.

See also: Arrays in Expressions, Looping Recipes

Parameters

Keyword Type Description

items

Any Type Array

An array or DataSubset containing the items to iterate over.

expression

Any Type

An expression that will be evaluated for each item. See Usage considerations for more information.

Returns

Any Type Array

Usage considerations

Function variables

The following function variables are available when configuring the expression input:

  • fv!item (Any Type): The current item
  • fv!index (Integer): The current item's index in the items array
  • fv!identifer (Any Type Array): When items is a DataSubset with identifiers, the current item's identifier, otherwise null
  • fv!isFirst (Boolean): True for the first item in the items array, otherwise false
  • fv!isLast (Boolean): True for the last item in the items array, otherwise false
  • fv!itemCount (Integer): The total number of items (including nulls)

Using the items parameter

When items is null or an empty list, a!forEach() returns an empty list of the same type as items. It does not evaluate the expression in these cases.

a!forEach(items: null, expression: length(fv!item)) returns {}

When items is passed a DataSubset:

  • a!forEach() iterates through the DataSubset's data field.
  • If the DataSubset's identifiers are populated, it must be an array of unique items and must be the same length as the data field.
  • When present in an interface, DataSubset identifiers are used to associate local variables with particular rows.

a!forEach(items: a!dataSubset(data: {1, 2, 3 }), expression: fv!item + 2) returns {3, 4, 5}

If a two-dimensional array is passed to the items parameter, a!forEach() evaluates the expression once for each item in the outer array. In these cases fv!item may be an array.

a!forEach(items: merge({1,2}, {10,20}), expression: fv!item[1] + fv!item[2]) returns {11, 22}

fv!item is always cast to its runtime type and will not appear to be Any Type even if that is what was passed in to items.

a!forEach(items: {1, "hello"}, expression: typename(typeof(fv!item))) returns {"Number (Integer)", "Text"}

Using the expression parameter

The expression parameter can be configured with any valid expression, including any number of rules, functions, constants, etc.

a!forEach(items: {1, null, 3}, expression: if(isnull(fv!item), "No Value", "Value: " & fv!item)) returns {"Value: 1", "No Value", "Value: 3"}

If the expression parameter contains a data query, each loop iteration may be evaluated in parallel to reduce the overall evaluation time.

The result of each expression evaluation is appended to the returned list in the same order as the corresponding item in items.

a!forEach(items: {100, 200, 300}, expression: fv!item + 1) returns {101, 201, 301}

When passed a single non-null value that is not a DataSubset, a!forEach() evaluates the expression once for that value and returns the result in a single-item list.

a!forEach(items: 3, expression: fv!item + 1) returns {4}

If the result of any expression is an array, a!forEach() returns a two-dimensional array. Two-dimensional arrays can be useful when processing data, but not all functions support them. Two-dimensional arrays are auto-flattened into one-dimensional arrays upon being stored in a process variable, node input, typed rule input, or custom data type field. Local variables, however, can store the two-dimensional array without flattening them.

a!forEach(items: {1, 2, 3}, expression: enumerate(fv!item))) returns a 3 item list consisting of {0}, {0, 1}, and {0, 1, 2}

You can use a!flatten() on the result of a!forEach() to convert to a one-dimensional array.

Examples

Use the same variable multiple times

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concat(
  a!forEach(
  items: {"the", "variables", "fv!isFirst", "and", "fv!isLast", "are", "helpful"},
    expression: concat(
      if(
        fv!isFirst,
        proper(fv!item),
        fv!item
      ),
      if(
        fv!isLast,
        "!",
        " "
      )
    )
  )
)

returns: "The variables fv!isFirst and fv!isLast are helpful!"

Using multiple function variables

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a!forEach(
  items: {"apple", "pear", "banana"},
  expression: "Word " & fv!index & " is length: " & len(fv!item)
)

returns: {"Word 1 is length: 5", "Word 2 is length: 4", "Word 3 is length: 6"}

Using a!forEach with interface components

In the interface, the expression parameter can contain interface components, a!localVariables() variables, and load() variables. To edit the current array item, interface components should save values into fv!item instead of indexing back into the original array so that a!forEach() can keep local variables associated with the correct rows.

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a!localVariables(
  local!names: {"Alice", "Bob", "Carol"},
  a!forEach(
    items: local!names,
    expression: a!localVariables(
      local!modified,
      a!textField(
        instructions: if(local!modified, "Modified!", ""),
        value: fv!item,
        saveInto: {
          fv!item,
          a!save(local!modified, true)
        }
      )
    )
  )
)

If the original array needs to be modified without writing to fv!item, either because it is being changed outside the a!forEach() loop or because a loop iteration is modifying an item besides the current one, then use a DataSubset with identifiers to make sure local variables are associated with the correct rows.

Nesting a!forEach

If you need to nest an a!forEach() inside another a!forEach() and want to refer to the outer fv!item, you can either put it in a local variable before calling the second a!forEach() or put the inner call in a separate rule and pass in fv!item via a rule input. For example:

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a!forEach(
  items: {"January", "February", "March"},
  expression: a!localVariables(
    local!month: fv!item,
    a!forEach(
      items: {1, 15},
      expression: local!month & " " & fv!item
    )
  )
)

The above expression returns a three item list containing {"January 1", "January 15"}, {"February 1", "February 15"}, and {"March 1", "March 15"}

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