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KeyComplement
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KeyComplement

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KeyComplement[{assocall,assoc1,assoc2,…}]

generates an association in which only elements whose keys appear in assocall but not in any of the associ are retained.

Details and Options

  • KeyComplement preserves the order of the elements in assocall.
  • KeyComplement can be used not only on Association objects, but also on lists of rules.
  • KeyComplement[{assocall, assoc1, …}, SameTesttest] applies test to each pair of keys of the elements in assocall and the associ to determine whether they should be considered the same.

Examples

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Basic Examples  (4)Summary of the most common use cases

Find a key that is not present elsewhere:

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In[1]:=1
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https://wolfram.com/xid/09ckdtwi6-cbxxtv
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Out[1]=1
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In[2]:=2
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https://wolfram.com/xid/09ckdtwi6-wxrq0
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Out[2]=2
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In[3]:=3
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https://wolfram.com/xid/09ckdtwi6-ulkjw
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Out[3]=3

Filter a list of rules:

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In[1]:=1
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https://wolfram.com/xid/09ckdtwi6-b8dqo6
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Out[1]=1

A single element of a list remains unchanged:

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In[1]:=1
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https://wolfram.com/xid/09ckdtwi6-g4cn30
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Out[1]=1

A list of rules is converted to an Association:

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In[2]:=2
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https://wolfram.com/xid/09ckdtwi6-b0a2qo
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Out[2]=2

Use a custom comparison function to compare keys:

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In[1]:=1
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https://wolfram.com/xid/09ckdtwi6-bv1pbc
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Out[1]=1

Possible Issues  (2)Common pitfalls and unexpected behavior

A single Rule element is automatically wrapped in a List:

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In[1]:=1
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https://wolfram.com/xid/09ckdtwi6-dtee3k
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Out[1]=1
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In[2]:=2
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https://wolfram.com/xid/09ckdtwi6-gx923
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Out[2]=2

These are the same as the following:

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In[3]:=3
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https://wolfram.com/xid/09ckdtwi6-fqhb9
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Out[3]=3

A list with no elements is not accepted:

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In[1]:=1
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https://wolfram.com/xid/09ckdtwi6-dqbf6g
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Out[1]=1
Wolfram Research (2015), KeyComplement, Wolfram Language function, https://reference.wolfram.com/language/ref/KeyComplement.html.
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Wolfram Research (2015), KeyComplement, Wolfram Language function, https://reference.wolfram.com/language/ref/KeyComplement.html.

Text

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

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

CMS

Wolfram Language. 2015. "KeyComplement." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/KeyComplement.html.

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Wolfram Language. 2015. "KeyComplement." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/KeyComplement.html.

APA

Wolfram Language. (2015). KeyComplement. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/KeyComplement.html

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Wolfram Language. (2015). KeyComplement. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/KeyComplement.html

BibTeX

@misc{reference.wolfram_2025_keycomplement, author="Wolfram Research", title="{KeyComplement}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/KeyComplement.html}", note=[Accessed: 26-March-2025 ]}

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@misc{reference.wolfram_2025_keycomplement, author="Wolfram Research", title="{KeyComplement}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/KeyComplement.html}", note=[Accessed: 26-March-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_keycomplement, organization={Wolfram Research}, title={KeyComplement}, year={2015}, url={https://reference.wolfram.com/language/ref/KeyComplement.html}, note=[Accessed: 26-March-2025 ]}

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@online{reference.wolfram_2025_keycomplement, organization={Wolfram Research}, title={KeyComplement}, year={2015}, url={https://reference.wolfram.com/language/ref/KeyComplement.html}, note=[Accessed: 26-March-2025 ]}