RepeatedNull

p... or RepeatedNull[p]

is a pattern object that represents a sequence of zero or more expressions, each matching p.

RepeatedNull[p,max]

represents from 0 to max expressions matching p.

RepeatedNull[p,{min,max}]

represents between min and max expressions matching p.

RepeatedNull[p,{n}]

represents exactly n expressions matching p.

Details

  • p... can appear as an argument of any function. It represents any sequence of arguments.
  • All the objects in the sequence represented by p... must match p, but the objects need not be identical.
  • The expression p may, but need not, itself be a pattern object.

Examples

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Basic Examples  (2)

Replace any list of zero or more a's by x:

Replace any list of zero or more f's with one argument:

Scope  (6)

a... represents a sequence of a's inside any head:

Replace any list of a's with lengths between 0 and 3:

Replace any list of a's with lengths between 2 and 3:

Replace lists with lengths between 0 and 2 elements:

Replace lists with 0 to 3 identical elements:

Require only part of the pattern to be the same throughout the sequence:

Properties & Relations  (4)

RepeatedNull[p] or p... is equivalent to RepeatedNull[p,{0,Infinity}]:

RepeatedNull[p,max] is equivalent to RepeatedNull[p,{0,max}]:

RepeatedNull[p] and RepeatedNull[p,max] allow zero repeats:

Repeated[p] and Repeated[p,max] require at least one repeat:

The forms RepeatedNull[p,{min,max}] and Repeated[p,{min,max}] are equivalent:

So are the forms RepeatedNull[p,{n}] and Repeated[p,{n}]:

Possible Issues  (1)

A repeated named pattern will only match a sequence of identical repeats:

A repeated unnamed pattern can match a sequence of nonidentical elements:

Wolfram Research (1988), RepeatedNull, Wolfram Language function, https://reference.wolfram.com/language/ref/RepeatedNull.html (updated 2007).

Text

Wolfram Research (1988), RepeatedNull, Wolfram Language function, https://reference.wolfram.com/language/ref/RepeatedNull.html (updated 2007).

BibTeX

@misc{reference.wolfram_2021_repeatednull, author="Wolfram Research", title="{RepeatedNull}", year="2007", howpublished="\url{https://reference.wolfram.com/language/ref/RepeatedNull.html}", note=[Accessed: 13-June-2021 ]}

BibLaTeX

@online{reference.wolfram_2021_repeatednull, organization={Wolfram Research}, title={RepeatedNull}, year={2007}, url={https://reference.wolfram.com/language/ref/RepeatedNull.html}, note=[Accessed: 13-June-2021 ]}

CMS

Wolfram Language. 1988. "RepeatedNull." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2007. https://reference.wolfram.com/language/ref/RepeatedNull.html.

APA

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