### Atom - `Ġ`

- Group Indices by Value

Characters: `Ġ`

Tags: `array`

##### Arity: monadic

This atom is monadic, which means it takes one argument.

##### Functionality

Group the indices of a list by the corresponding values.

##### Details

This returns a list of lists. Each number in `[1, 2, ..., len(z)]`

will appear exactly once. Each sub-list will contain indices that map to the same value; that is, `i`

and `j`

are in the same sublist if and only if `z[i] == z[j]`

. The sublists are ordered by the element they correspond to.