This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.

# 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 in by newn. ReplacePart[expr, {i, j, ...}->new]replaces the part at position {i, j, ...}. ReplacePart[expr, {{i1, j1, ...}->new1, ...}]replaces parts at positions {in, jn, ...} by newn. ReplacePart[expr, {{i1, j1, ...}, ...}->new]replaces all parts at positions {in, jn, ...} by new.
• Explicit negative part numbers count from the end.  »
• Part position specifications can be patterns.
• Each pattern is effectively tested against each list of part numbers for parts in expr.
• Patterns p (such as x_) that are not explicitly lists are treated as {p}.
• 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 , a head is replaced only when the corresponding position specification is explicitly 0.
• With a head is replaced whenever the corresponding position specification matches 0.
Replace part 3:
 Out[1]=

Replace parts 2 and 5:
 Out[1]=

Replace part of an array:
 Out[1]=

Replace parts whose positions match a pattern:
 Out[1]=

Replace parts in any expression:
 Out[1]=
 Scope   (8)
 Options   (3)
 Applications   (8)