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Mathematica > Parts of Expressions >

Built-in Mathematica Symbol

ReplacePart

ReplacePart[expr, i->new]
yields an expression in which the i

part of expr is replaced by new.

ReplacePart[expr, {i₁->new₁, i₂->new₂, ...}]
replaces parts at positions i_n by new_n.

ReplacePart[expr, {i, j, ...}->new]
replaces the part at position {i, j, ...}.

ReplacePart[expr, {{i₁, j₁, ...}->new₁, ...}]
replaces parts at positions {i_n, j_n, ...} by new_n.

ReplacePart[expr, {{i₁, j₁, ...}, ...}->new]
replaces all parts at positions {i_n, j_n, ...} by new.

Each pattern is effectively tested against each list of part numbers for parts in expr.

Patterns can include constructs such as __, representing position specifications of variable lengths.

ReplacePart[expr, i:>new] can be used to replace a part without first evaluating it. With a rule such as patt:>new, new is evaluated separately for each position that matches patt.

With the default option setting Heads->Automatic, a head is replaced only when the corresponding position specification is explicitly 0.

With Heads->True a head is replaced whenever the corresponding position specification matches 0.

Replace part 3:

Replace parts 2 and 5:

Replace part

of an array:

Replace parts whose positions match a pattern:

Replace parts in any expression: