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Which
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Which

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Which[test1,value1,test2,value2,…]

evaluates each of the testi in turn, returning the value of the valuei corresponding to the first one that yields True.

Details

  • Which has attribute HoldAll.
  • If any of the testi evaluated by Which give neither True nor False, then a Which object containing these remaining elements is returned unevaluated. »
  • You can make Which return a "default value" by taking the last testi to be True.
  • If all the testi evaluate to False, Which returns Null.

Examples

open allclose all

Basic Examples  (1)Summary of the most common use cases

In[1]:=1
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https://wolfram.com/xid/0binpz92-bqbdxr
Out[1]=1

Scope  (4)Survey of the scope of standard use cases

Programming Behavior  (3)

Which can be maintained in symbolic form:

In[1]:=1
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https://wolfram.com/xid/0binpz92-dhl9dl
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0binpz92-l7lis
Out[2]=2

Conditions are evaluated until one is found that is neither True nor False:

In[1]:=1
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https://wolfram.com/xid/0binpz92-ijkmky
Out[1]=1

Use True for an else clause that always matches:

In[1]:=1
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https://wolfram.com/xid/0binpz92-0ywjq5
In[2]:=2
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https://wolfram.com/xid/0binpz92-dwhp6j
Out[2]=2

Symbolic Transformations  (1)

Define a piecewise function:

In[1]:=1
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https://wolfram.com/xid/0binpz92-k3irbe
Out[1]=1

Expand it to use Piecewise:

In[2]:=2
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https://wolfram.com/xid/0binpz92-7fdp3
Out[2]=2

Do symbolic operations:

In[3]:=3
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https://wolfram.com/xid/0binpz92-gy70lb
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0binpz92-brjttk
Out[4]=4
In[5]:=5
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https://wolfram.com/xid/0binpz92-f86ls1
Out[5]=5
In[6]:=6
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https://wolfram.com/xid/0binpz92-c41afg
Out[6]=6

Properties & Relations  (2)Properties of the function, and connections to other functions

Use Which rather than a nested if-then-elseif chain:

In[1]:=1
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https://wolfram.com/xid/0binpz92-iwoavx
In[2]:=2
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https://wolfram.com/xid/0binpz92-bqb1ti
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0binpz92-i0gxyp
In[4]:=4
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https://wolfram.com/xid/0binpz92-gmohah
Out[4]=4

Use PiecewiseExpand to convert Which to Piecewise:

In[1]:=1
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https://wolfram.com/xid/0binpz92-gl01e8
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0binpz92-wfdrf
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0binpz92-cai747
Out[3]=3
Wolfram Research (1988), Which, Wolfram Language function, https://reference.wolfram.com/language/ref/Which.html.
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Wolfram Research (1988), Which, Wolfram Language function, https://reference.wolfram.com/language/ref/Which.html.

Text

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

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

CMS

Wolfram Language. 1988. "Which." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Which.html.

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Wolfram Language. 1988. "Which." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Which.html.

APA

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

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

BibTeX

@misc{reference.wolfram_2025_which, author="Wolfram Research", title="{Which}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/Which.html}", note=[Accessed: 20-June-2025 ]}

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@misc{reference.wolfram_2025_which, author="Wolfram Research", title="{Which}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/Which.html}", note=[Accessed: 20-June-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_which, organization={Wolfram Research}, title={Which}, year={1988}, url={https://reference.wolfram.com/language/ref/Which.html}, note=[Accessed: 20-June-2025 ]}

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@online{reference.wolfram_2025_which, organization={Wolfram Research}, title={Which}, year={1988}, url={https://reference.wolfram.com/language/ref/Which.html}, note=[Accessed: 20-June-2025 ]}