Select

Select[data,crit]

picks out all elements ei of data for which crit[ei] is True.

Select[data,critprop]

returns the property prop of the selected elements.

Select[data,crit,n]

picks out the first n elements for which crit[ei] is True.

Select[crit]

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

Details

  • Select keeps the elements for which the given criterion crit is True.
  • The data can have the following additional forms and interpretations:
  • {e1,e2,…}list of values »
    f[e1,e2,…]expression with any head f »
    Association[…]association of values »
    QuantityArray[…]quantity array or other structured array
    Tabular[…]type-consistent tabular data »
    TabularColumn[…]type-consistent column data »
    Dataset[…]general hierarchical data
  • The property prop can have the following forms and interpretations:
  • "Element"the selected values »
    "Index"indices of the selected values »
    "BitVectorMask"Boolean mask returning True for slected values and False otherwise »
    {prop1,prop2,…}a list of multiple forms »
    Allan association giving element, index and bit vector mask »
  • Select[crit][data] is equivalent to Select[data,crit].
  • Parallelize[Select[data,crit]] or ParallelSelect[data,crit] computes Select[data,crit] in parallel on all subkernels. »

Examples

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Basic Examples  (6)

Select elements that are even:

Return the indices of the selected elements:

Return only the first expression selected:

Use the operator form of Select:

Select operates on values in an Association:

Select rows in a Tabular object:

Scope  (15)

Basic Uses  (5)

Find pairs containing x:

Find up to 2 pairs containing x:

Fewer than the requested elements may be returned:

Use a pure function to test each element:

Use an operator form as selection criterion:

Use Select in operator form:

Input Data  (5)

Select works with any head, not just List:

Select works on values in Association:

Select works with SparseArray objects:

The result may be a list if it is not sparse:

Select works with TabularColumn objects:

Select all dates in November:

The distribution of the dates is uniform:

Use Select on a Tabular object with named columns:

Select rows with last column date being a business day:

Property Forms  (5)

Return the selected elements:

Return the indices of the selected elements:

Return the Boolean mask of the data:

Return two forms:

Return the association with all the properties:

Applications  (7)

Select numbers up to 100 that equal 1 modulo both 3 and 5:

Select 4-tuples that read the same in reverse:

Find the first four 3×3 matrices of 0s and 1s that have determinant 1:

Select eigenvalues that lie within the unit circle:

Find built-in Wolfram Language objects whose names are less than 3 characters long:

Select numeric quantities from a product:

Find an approximation to by finding the proportion of points that lie within a disk:

Properties & Relations  (4)

Select is complementary to Discard:

Select is similar to Cases except that it uses a function instead of a pattern:

Select the lists that have sum of elements less than 10:

Use Cases to get the same result:

Select elements that are even:

Use GatherBy to separate odd and even elements:

Use GroupBy to construct an association explicitly containing as keys the results of the criterion:

Compute Select in parallel:

Possible Issues  (2)

Select picks out elements for which applying the criterion explicitly yields True:

The symbolic object x is not included in either case, since neither inequality gives True:

The head of the input expression is only preserved for the default "Element" property:

Wolfram Research (1988), Select, Wolfram Language function, https://reference.wolfram.com/language/ref/Select.html (updated 2025).

Text

Wolfram Research (1988), Select, Wolfram Language function, https://reference.wolfram.com/language/ref/Select.html (updated 2025).

CMS

Wolfram Language. 1988. "Select." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2025. https://reference.wolfram.com/language/ref/Select.html.

APA

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

BibTeX

@misc{reference.wolfram_2024_select, author="Wolfram Research", title="{Select}", year="2025", howpublished="\url{https://reference.wolfram.com/language/ref/Select.html}", note=[Accessed: 17-January-2025 ]}

BibLaTeX

@online{reference.wolfram_2024_select, organization={Wolfram Research}, title={Select}, year={2025}, url={https://reference.wolfram.com/language/ref/Select.html}, note=[Accessed: 17-January-2025 ]}