BUILT-IN MATHEMATICA SYMBOL

# Replace

Replace[expr, rules]
applies a rule or list of rules in an attempt to transform the entire expression expr.

Replace[expr, rules, levelspec]
applies rules to parts of expr specified by levelspec.

## Details and OptionsDetails and Options

• The rules must be of the form or .
• A list of rules can be given. The rules are tried in order. The result of the first one that applies is returned. If none of the rules apply, the original expr is returned.
• If the rules are given in nested lists, Replace is effectively mapped onto the inner lists. Thus Replace[expr, {{r11, r12}, {r21, ...}, ...}] is equivalent to .
• Delayed rules defined with can contain conditions.
• Replace uses standard level specifications:
•  n levels through n Infinity levels through Infinity {n} level n only {n1,n2} levels through
• The default value for levelspec in Replace is , corresponding to the whole expression.
• A positive level n consists of all parts of expr specified by n indices.
• A negative level -n consists of all parts of expr with depth n.
• Level consists of numbers, symbols, and other objects that do not have subparts.
• With the option setting , Replace includes heads of expressions, and their parts.
• Replacements are performed to parts specified by levelspec even when those parts have Hold or related wrappers.

## ExamplesExamplesopen allclose all

### Basic Examples (2)Basic Examples (2)

Replace by default applies rules only to complete expressions:

 Out[1]=

It does not map down to subparts:

 Out[2]=

A list of rules gives a list of results:

 Out[1]=