ReplacePart

ReplacePart(expr, i -> new)

replaces part i in expr with new.

ReplacePart(expr, {{i, j} -> e1, {k, l} -> e2})'

replaces parts i and j with e1, and parts k and l with e2.

Examples

>> ReplacePart({a, b, c}, 1 -> t)
{t,b,c}

>> ReplacePart({{a, b}, {c, d}}, {2, 1} -> t)
{{a,b},{t,d}}

>> ReplacePart({{a, b}, {c, d}}, {{2, 1} -> t, {1, 1} -> t})
{{t,b},{t,d}}

>> ReplacePart({a, b, c}, {{1}, {2}} -> t)
{t,t,c}

Delayed rules are evaluated once for each replacement:

>> n = 1
>> ReplacePart({a, b, c, d}, {{1}, {3}} :> n++)
{1,b,2,d}

Non-existing parts are simply ignored:

>> ReplacePart({a, b, c}, 4 -> t)
{a,b,c}

You can replace heads by replacing part 0:

>> ReplacePart({a, b, c}, 0 -> Times)
a*b*c

Negative part numbers count from the end:

>> ReplacePart({a, b, c}, -1 -> t)
{a,b,t}

Related terms

Replace, ReplaceAll, ReplaceList, ReplaceRepeated

Implementation status

• ✅ - full supported

Github

• Implementation of ReplacePart