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CountDistinct[list]

gives the number of distinct elements that appear in list.

CountDistinct[list,test]

applies test to pairs of elements to determine whether they should be considered equivalent.

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CountDistinct

CountDistinct[list]

gives the number of distinct elements that appear in list.

CountDistinct[list,test]

applies test to pairs of elements to determine whether they should be considered equivalent.

Details

Examples

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Basic Examples  (2)

Count distinct elements in a list:

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

Count distinct values in an association:

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

Scope  (2)

The list need not have head List:

Wolfram Language code: CountDistinct[Hold[1 + 2, 4 - 1, 1 + 2, 2 + 1]]

Treat numbers as equal if they differ by 0.01 or less:

Wolfram Language code: CountDistinct[{3.0, 3.1, 3.11, 3.5, 3.51}, Abs[#1 - #2] <= 0.01&]

Applications  (1)

Count the number of distinct characters that occur in a string:

Wolfram Language code: CountDistinct[Characters["It was the best of times, it was the worst of times"]]

Properties & Relations  (3)

CountDistinct[list] is equivalent to CountDistinct[list,SameQ]:

Wolfram Language code: list = Join[RandomInteger[100, {50}], RandomReal[1, {50}], {x, y, z, π, E}];
Wolfram Language code: CountDistinct[list] == CountDistinct[list, SameQ]

CountDistinct[list] is equivalent to Length[DeleteDuplicates[list]]:

Wolfram Language code: list = RandomInteger[100, {33}];
Wolfram Language code: CountDistinct[list] == Length[DeleteDuplicates[list]]

CountDistinct[list,test] is equivalent to Length[DeleteDuplicates[list,test]]:

Wolfram Language code: lastDigitSameQ[x_, y_] := Mod[x, 10] === Mod[y, 10]
Wolfram Language code: CountDistinct[list, lastDigitSameQ] == Length[DeleteDuplicates[list, lastDigitSameQ]]

CountDistinct[list,test] applies test to two elements to determine if they are equivalent:

Wolfram Language code: CountDistinct[{{a, x}, {a, y}, {b, z}}, First[#] == First[#2]&]

CountDistinctBy[list,f] applies the transformation f to each element, then compares the results:

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

Possible Issues  (1)

If the comparison function returns neither True nor False, elements are assumed to be distinct:

Wolfram Language code: CountDistinct[{4, 4, 4}, f]

Compare with the function that always reports elements as distinct:

Wolfram Language code: CountDistinct[{4, 4, 4}, False&]
Wolfram Research (2014), CountDistinct, Wolfram Language function, https://reference.wolfram.com/language/ref/CountDistinct.html (updated 2024).

Text

Wolfram Research (2014), CountDistinct, Wolfram Language function, https://reference.wolfram.com/language/ref/CountDistinct.html (updated 2024).

CMS

Wolfram Language. 2014. "CountDistinct." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2024. https://reference.wolfram.com/language/ref/CountDistinct.html.

APA

Wolfram Language. (2014). CountDistinct. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/CountDistinct.html

BibTeX

@misc{reference.wolfram_2026_countdistinct, author="Wolfram Research", title="{CountDistinct}", year="2024", howpublished="\url{https://reference.wolfram.com/language/ref/CountDistinct.html}", note=[Accessed: 13-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_countdistinct, organization={Wolfram Research}, title={CountDistinct}, year={2024}, url={https://reference.wolfram.com/language/ref/CountDistinct.html}, note=[Accessed: 13-June-2026]}