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ReplaceRepeated
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ReplaceRepeated

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expr//.rules

repeatedly performs replacements until expr no longer changes.

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represents an operator form of ReplaceRepeated that can be applied to an expression.

Details and Options

  • expr//.rules effectively applies /. repeatedly, until the results it gets no longer change.
  • It performs one complete pass over the expression using /., then carries out the next pass.
  • You should be very careful to avoid infinite loops when you use the //. operator. The command x//.x->x+1 will, for example, lead to an infinite loop.
  • ReplaceRepeated takes the option MaxIterations, which specifies the maximum number of times it will try to apply the rules you give. The default setting is MaxIterations->65536. With MaxIterations->Infinity there is no limit.
  • ReplaceRepeated[rules][expr] is equivalent to ReplaceRepeated[expr,rules].

Examples

open allclose all

Basic Examples  (3)Summary of the most common use cases

Apply rules for the power and product laws for logarithms of real numbers recursively:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-h4kzb4
In[2]:=2
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https://wolfram.com/xid/0h2n4bbur6-dybzai
Out[2]=2

ReplaceAll does just a single replacement:

In[3]:=3
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https://wolfram.com/xid/0h2n4bbur6-f7bsez
Out[3]=3

Remove all occurrences of a head, including nested ones:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-lmujfj
Out[1]=1

ReplaceAll would only remove the outermost head:

In[2]:=2
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https://wolfram.com/xid/0h2n4bbur6-k9yfsm
Out[2]=2

Use ReplaceRepeated in operator form:

In[1]:=1
✖
https://wolfram.com/xid/0h2n4bbur6-836t6x
Out[1]=1

Scope  (3)Survey of the scope of standard use cases

If no rule matches, the input expression is returned:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-qwluyq
Out[1]=1

Replace occurrences of f with 1 followed by exactly one integer:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-nnbph7
Out[1]=1

Replace occurrences of f with 1 followed by one or more integers:

In[2]:=2
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https://wolfram.com/xid/0h2n4bbur6-j63gmn
Out[2]=2

Replace occurrences of f with 1 followed by zero or more integers:

In[3]:=3
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https://wolfram.com/xid/0h2n4bbur6-80fhzf
Out[3]=3

ReplaceRepeated works inside held expressions:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-icn15m
Out[1]=1

Do not evaluate the right-hand side of the rule before doing the replacement:

In[2]:=2
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https://wolfram.com/xid/0h2n4bbur6-d4rf13
Out[2]=2

Evaluate the right-hand side before replacement:

In[3]:=3
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https://wolfram.com/xid/0h2n4bbur6-35kafs
Out[3]=3

Applications  (1)Sample problems that can be solved with this function

Undo "currying" of function arguments:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-p9
Out[1]=1

Properties & Relations  (5)Properties of the function, and connections to other functions

An empty list is considered to have no matching rules:

In[1]:=1
✖
https://wolfram.com/xid/0h2n4bbur6-bm5026
Out[1]=1

When a list of lists is used for replacement, the result is a list of the same length:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-uie9dq
Out[1]=1

Evaluation is not forced when replacing into a held expression:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-pfw68a
Out[1]=1

ReplaceRepeated is effectively a combination of ReplaceAll and FixedPoint:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-cqlakc
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0h2n4bbur6-lrfw76
Out[2]=2

ReplaceRepeated scans multiple times from the top of an expression:

In[1]:=1
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https://wolfram.com/xid/0h2n4bbur6-s30uro
In[2]:=2
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https://wolfram.com/xid/0h2n4bbur6-8x5i4p
Out[2]=2

ReplaceAll replaces the largest subexpressions it can and then stops:

In[3]:=3
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https://wolfram.com/xid/0h2n4bbur6-04ppi7
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0h2n4bbur6-g7tdsa
Out[4]=4

Replace with level spec All will attempt to replace every subexpression exactly once:

In[5]:=5
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https://wolfram.com/xid/0h2n4bbur6-et2u4c
Out[5]=5
Wolfram Research (1988), ReplaceRepeated, Wolfram Language function, https://reference.wolfram.com/language/ref/ReplaceRepeated.html (updated 2018).
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Wolfram Research (1988), ReplaceRepeated, Wolfram Language function, https://reference.wolfram.com/language/ref/ReplaceRepeated.html (updated 2018).

Text

Wolfram Research (1988), ReplaceRepeated, Wolfram Language function, https://reference.wolfram.com/language/ref/ReplaceRepeated.html (updated 2018).

✖
Wolfram Research (1988), ReplaceRepeated, Wolfram Language function, https://reference.wolfram.com/language/ref/ReplaceRepeated.html (updated 2018).

CMS

Wolfram Language. 1988. "ReplaceRepeated." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2018. https://reference.wolfram.com/language/ref/ReplaceRepeated.html.

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Wolfram Language. 1988. "ReplaceRepeated." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2018. https://reference.wolfram.com/language/ref/ReplaceRepeated.html.

APA

Wolfram Language. (1988). ReplaceRepeated. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ReplaceRepeated.html

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Wolfram Language. (1988). ReplaceRepeated. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ReplaceRepeated.html

BibTeX

@misc{reference.wolfram_2025_replacerepeated, author="Wolfram Research", title="{ReplaceRepeated}", year="2018", howpublished="\url{https://reference.wolfram.com/language/ref/ReplaceRepeated.html}", note=[Accessed: 20-June-2025 ]}

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@misc{reference.wolfram_2025_replacerepeated, author="Wolfram Research", title="{ReplaceRepeated}", year="2018", howpublished="\url{https://reference.wolfram.com/language/ref/ReplaceRepeated.html}", note=[Accessed: 20-June-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_replacerepeated, organization={Wolfram Research}, title={ReplaceRepeated}, year={2018}, url={https://reference.wolfram.com/language/ref/ReplaceRepeated.html}, note=[Accessed: 20-June-2025 ]}

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@online{reference.wolfram_2025_replacerepeated, organization={Wolfram Research}, title={ReplaceRepeated}, year={2018}, url={https://reference.wolfram.com/language/ref/ReplaceRepeated.html}, note=[Accessed: 20-June-2025 ]}