Function

reduce( function, initial, list, context )

Calls a rule or function for each item in a list, passing the result of each call to the next one, and returns the value of the last computation.

Parameters

Returns

Any Type

Usage considerations

Referencing expressions and rules

Use fn!functionName or a!functionName to reference an expression function and rule!ruleName to reference a rule.

The initial accumulator value is given by initial.

Using rules or functions with multiple arguments

To use rules or functions that take more than two arguments, use the merge() function. For example, given a rule g(x, y, z), reduce(rule!g, i, merge({a, b, c}, {d, e, f})) returns g(g(g(i, a, d), b, e), c, f).

Understanding results

Returns a scalar value if the function called returns a scalar, and returns a list if the function called returns a list.

Limitations

Best used when the computation of each operation needs to use the result from the previous operation such as when the result of each operation is an array that should be appended to each other in order. The result from the previous operation is then passed to the subsequent operation as the parameter initial.

a!forEach() cannot be used within rules used in this function.

Examples

Generalized behavior

Given a function h(x, y), reduce(fn!h,initial, {a, b, c}, v) returns h(h(h(initial, a, v), b, v), c, v).

Substitute multiple values from initialValue

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reduce(
  fn!substitute,
  "abcdefg",
  {"a", "d", "f"},
  "#"
)

Returns "#bc#e#g". The function firsts replaces "a" from the initialValue. Then "d" is replaced from the result of the previous substitution. And finally the "f" is replaced.

Create new list from initial value

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reduce(
  fn!insert,
  {1},
  {2, 3},
  1
)

Returns {3, 2, 1}. The function firsts inserts 2 at the first position and then inserts 3 into the first position of the resulting list from the first insert.

Feature compatibility