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First[expr]

gives the first element in expr.

First[expr,def]

gives the first element if it exists, or def otherwise.

Details
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Examples  
Basic Examples  
Generalizations & Extensions  
Properties & Relations  
Possible Issues  
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First

First[expr]

gives the first element in expr.

First[expr,def]

gives the first element if it exists, or def otherwise.

Details

  • First[expr] is equivalent to expr[[1]].
  • First has attribute HoldRest. In First[expr,def], def is evaluated only if it is to be returned.

Examples

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Basic Examples  (5)

Extract the first element of a list:

Wolfram Language code: First[{a, b, c}]

Extract the first row of a matrix:

Wolfram Language code: First[{{a, b}, {c, d}}]

Extract the first element of an association:

Wolfram Language code: First[<|1 -> a, 2 -> b|>]

The head need not be List:

Wolfram Language code: First[a ^ 2 + b ^ 2]

Return x if there are zero elements:

Wolfram Language code: First[{}, x]
Wolfram Language code: First[{a, b}, x]

Generalizations & Extensions  (2)

First works on SparseArray objects:

Wolfram Language code: First[SparseArray[Range[100]]]

First extracts the first value in an Association:

Wolfram Language code: First[<|a -> x, b -> y|>]

Properties & Relations  (1)

First[expr] is equivalent to expr[[1]]:

Wolfram Language code: First[{a, b, c}]
Wolfram Language code: {a, b, c}[[1]]

Possible Issues  (2)

The expression is evaluated before First is applied:

Wolfram Language code: First[b ^ 2 + a ^ 2]

First always operates on the FullForm of expressions:

Wolfram Language code: First[1 / a ^ 2]
Wolfram Language code: FullForm[1 / a ^ 2]
Wolfram Research (1988), First, Wolfram Language function, https://reference.wolfram.com/language/ref/First.html (updated 2015).

Text

Wolfram Research (1988), First, Wolfram Language function, https://reference.wolfram.com/language/ref/First.html (updated 2015).

CMS

Wolfram Language. 1988. "First." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2015. https://reference.wolfram.com/language/ref/First.html.

APA

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

BibTeX

@misc{reference.wolfram_2026_first, author="Wolfram Research", title="{First}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/First.html}", note=[Accessed: 13-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_first, organization={Wolfram Research}, title={First}, year={2015}, url={https://reference.wolfram.com/language/ref/First.html}, note=[Accessed: 13-June-2026]}