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ContainsOnly
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ContainsOnly

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ContainsOnly[list1,list2]

yields True if list1 contains only elements that appear in list2.

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ContainsOnly[list2]

is an operator form that yields True when the object to which it is applied contains only elements that appear in list2.

Details and Options

Examples

open allclose all

Basic Examples  (2)Summary of the most common use cases

The first list contains only elements in the second list:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-tkz1cd
Out[1]=1

The first list contains elements not present in the second list:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-q4smkv
Out[1]=1

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

This is one of the longest English words containing only vowels:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-g1kme4
Out[1]=1

Use ContainsOnly in operator form:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-yhn4zc
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-vkve4c
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0btm8ukzwd8g-6eowz2
Out[3]=3

The number of songs composed either by John Lennon or Paul McCartney, or by both together:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-9cqisv
Out[1]=1

ContainsOnly works with associations:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-jtfkx9
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-oyyckd
Out[2]=2

Options  (2)Common values & functionality for each option

SameTest  (2)

By default, ContainsOnly considers elements to be the same if they are identical:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-va3try
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-m67or7
Out[2]=2

Changes of units are taken into account, as long as they represent the exact same quantity:

In[3]:=3
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https://wolfram.com/xid/0btm8ukzwd8g-jtl0vb
Out[3]=3

Numerical approximations are not considered as the same object:

In[4]:=4
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https://wolfram.com/xid/0btm8ukzwd8g-t34h5h
Out[4]=4

Use Equal as the comparison function to have numerical tolerance:

In[5]:=5
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https://wolfram.com/xid/0btm8ukzwd8g-gz6vvk
Out[5]=5

String comparisons are case sensitive by default:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-1pybm9
Out[1]=1

Convert to lower case before comparing:

In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-3b2q37
Out[2]=2

Applications  (1)Sample problems that can be solved with this function

Take the characters of a text, in lower case:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-kj61fv
Out[1]=1

They are all letters and basic punctuation symbols:

In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-rj2qjb
Out[2]=2

Properties & Relations  (3)Properties of the function, and connections to other functions

Reversing the arguments of ContainsOnly is equivalent to using ContainsAll:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-opnt8r
In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-py8oi3
In[3]:=3
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https://wolfram.com/xid/0btm8ukzwd8g-ehhrdi
Out[3]=3

ContainsOnly[list1,list2] is equivalent to SubsetQ[list2,list1]:

In[1]:=1
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https://wolfram.com/xid/0btm8ukzwd8g-3jdwr
In[2]:=2
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https://wolfram.com/xid/0btm8ukzwd8g-xyoj5b
In[3]:=3
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https://wolfram.com/xid/0btm8ukzwd8g-2gp42t
Out[3]=3

ContainsOnly[{},list] always returns True:

In[1]:=1
✖
https://wolfram.com/xid/0btm8ukzwd8g-2qq8ei
Out[1]=1
In[2]:=2
✖
https://wolfram.com/xid/0btm8ukzwd8g-uq27qr
Out[2]=2
Wolfram Research (2015), ContainsOnly, Wolfram Language function, https://reference.wolfram.com/language/ref/ContainsOnly.html.
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Wolfram Research (2015), ContainsOnly, Wolfram Language function, https://reference.wolfram.com/language/ref/ContainsOnly.html.

Text

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

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

CMS

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

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

APA

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

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

BibTeX

@misc{reference.wolfram_2025_containsonly, author="Wolfram Research", title="{ContainsOnly}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/ContainsOnly.html}", note=[Accessed: 20-June-2025 ]}

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@misc{reference.wolfram_2025_containsonly, author="Wolfram Research", title="{ContainsOnly}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/ContainsOnly.html}", note=[Accessed: 20-June-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_containsonly, organization={Wolfram Research}, title={ContainsOnly}, year={2015}, url={https://reference.wolfram.com/language/ref/ContainsOnly.html}, note=[Accessed: 20-June-2025 ]}

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@online{reference.wolfram_2025_containsonly, organization={Wolfram Research}, title={ContainsOnly}, year={2015}, url={https://reference.wolfram.com/language/ref/ContainsOnly.html}, note=[Accessed: 20-June-2025 ]}