index by

index items into a dict

(list xs, function f) -> any

Returns a dict that contains all values from xs. Each x in xs is indexed by key f(x).

If xs is a list:
If f accepts one argument, x is passed.
If f accepts two arguments, x and its index are passed.

If xs is a dict:
If f accepts one argument, each entry’s value is passed.
If f accepts two arguments, each entry’s value and key are passed.

The indexing function f must return a string, or a value that can be cast to string.

In case f(x) returns the same key for multiple x, only one of such x will be indexed in the returned dict. In such cases it is undefined which x is preserved in the returned dict.

In case f(x) returns nil the corresponding x is omitted from the result.

Returns nil if xs is nil.

Throws an error if xs is neither a list nor a dict.

Throws an error if f is nil.

Parameters