select_index()

Select one or more items from a list and return the list of indexes of the items.

Synopsis

select_index(list-expression, test)

Description

The first argument specifies a list from which indices are to be selected, while the second argument specifies a true-false expression.

This action returns a list consisting of the positions of all items in the first argument list for which the expression returns true. The special variable _ in the test refers to the list item being evaluated.

Parameters

list-expression

An expression that evaluates to the list to select from.

test

A true-false expression that us evaluated for each item in the list.

Returns

The function returns a list, which may be empty.

Examples

Select the indexes of the positive numbers from a list:

xlist = list(10, 0, -20, 0.5)
positives_index_list = select_index(x_list, _ > 0)
# positives_index_list = list(0, 3)

See Also

list(), find_index(), select()