Wolfram: List. Change Element

Replace Parts by Position

ReplacePart

Replace parts by Position .

• ReplacePart

(* replace second element by x *)
ReplacePart[ {a, b, c}, 2 -> x ]
(* {a, x, c} *)

(* replace second element by x *)
ReplacePart[ {a, {3, 4}, c}, 2 -> x ]
(* {a, x, c} *)

(* replace multiple positions *)
ReplacePart[ {a, b, c, d}, {2 -> x, 3 -> y} ]
(* {a, x, y, d} *)

(* replace element at position {2,1} by x *)
ReplacePart[ {a, {3, 4}, c}, {2,1} -> x ]
(* {a, {x, 4}, c} *)

Replace Parts by Position via Assignment

you can also modify a element by assignment.

var[[n]] = val

Assign a new value at index n in var. Note, expr[[n]] is shortcut for Part

• Part

xx = {a, b, c};
xx[[2]] = 4;
xx
(* {a, 4, c} *)

Replace Parts by Pattern

• Wolfram: Replace Expression by Pattern