WolframLang: Change Element in List
ReplacePart
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Replace by Pattern
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}
you can also modify a element by assignment.
var[[n]] = val
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Assign a new value at index n in var.
note,expr[[n]]
is shortcut forPart
Partxx = {a, b, c} xx[[2]] = 4 xx (* {a, 4, c} *)