Pick

is a dyadic primitive function which performs deep indexing on a possibly nested array. Pick allows to extract a value through multiple layers of nesting in a single function application. Pick uses the Right Shoe glyph.

Examples
The left argument X must be a scalar or vector where each element of X specifies the multi-dimensional index at each layer of the right argument Y. The result of  is the item of Y at the location specified by X.

Documentation

 * Dyalog
 * APLX