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DeleteAdjacentDuplicates[list]

deletes all duplicates in runs of identical elements in list.

DeleteAdjacentDuplicates[list,test]

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

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Basic Examples  
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DeleteAdjacentDuplicates

DeleteAdjacentDuplicates[list]

deletes all duplicates in runs of identical elements in list.

DeleteAdjacentDuplicates[list,test]

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

Details

Examples

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Basic Examples  (3)

Delete adjacent duplicated elements:

Wolfram Language code: DeleteAdjacentDuplicates[{3, 2, 2, 2, 3, 3, 1}]

Delete adjacent elements that coincide under Equal:

Wolfram Language code: DeleteAdjacentDuplicates[{3, 2., 2, 2`20, 3 / 2, 1.5, 1}, Equal]

Delete elements whose values duplicate those just before them in the association:

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

Scope  (2)

Delete elements unless they are larger than the preceding ones:

Wolfram Language code: DeleteAdjacentDuplicates[{1, 3, 5, 4, 3, 4, 1, 9, 9, 7, 8}, Greater]

In DeleteAdjacentDuplicates[list], list may be any nonatomic expression:

Wolfram Language code: DeleteAdjacentDuplicates[f[x, x, y, y, y, x, x, y, z]]

Properties & Relations  (2)

DeleteAdjacentDuplicates is similar to taking the first of each item from Split:

Wolfram Language code: list = RandomInteger[2, 20]
Wolfram Language code: Split[list][[All, 1]]
Wolfram Language code: DeleteAdjacentDuplicates[list]

Delete sublists that have the same total:

Wolfram Language code: list = {{1, 2}, {0, 3}, {1, 1}, {2, 0}, {2, 1}}
Wolfram Language code: DeleteAdjacentDuplicates[list, Total[#1] == Total[#2]&]

The equivalent operation can be achieved using SplitBy as well:

Wolfram Language code: SplitBy[list, Total][[All, 1]]
Wolfram Research (2022), DeleteAdjacentDuplicates, Wolfram Language function, https://reference.wolfram.com/language/ref/DeleteAdjacentDuplicates.html.

Text

Wolfram Research (2022), DeleteAdjacentDuplicates, Wolfram Language function, https://reference.wolfram.com/language/ref/DeleteAdjacentDuplicates.html.

CMS

Wolfram Language. 2022. "DeleteAdjacentDuplicates." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/DeleteAdjacentDuplicates.html.

APA

Wolfram Language. (2022). DeleteAdjacentDuplicates. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/DeleteAdjacentDuplicates.html

BibTeX

@misc{reference.wolfram_2026_deleteadjacentduplicates, author="Wolfram Research", title="{DeleteAdjacentDuplicates}", year="2022", howpublished="\url{https://reference.wolfram.com/language/ref/DeleteAdjacentDuplicates.html}", note=[Accessed: 13-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_deleteadjacentduplicates, organization={Wolfram Research}, title={DeleteAdjacentDuplicates}, year={2022}, url={https://reference.wolfram.com/language/ref/DeleteAdjacentDuplicates.html}, note=[Accessed: 13-June-2026]}