WolframLang: Change Element in List

By Xah Lee. Date: . Last updated: .

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 and 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

List