MapIndexed

MapIndexed[f, expr] applies f to the elements of expr, providing the position as a second argument.

MapIndexed[f, expr, levelspec] applies f to parts at specified levels.

Examples

Map with position information:

MapIndexed[f, {a, b, c}]
(* {f[a, {1}], f[b, {2}], f[c, {3}]} *)

Use position to label elements:

MapIndexed[{#2[[1]], #1} &, {a, b, c}]
(* {{1, a}, {2, b}, {3, c}} *)

Please visit the official Wolfram Language Reference for more details.