Part

or Part[expr, i]
gives the i^(th) part of expr.


counts from the end.

or Part[expr, i, j, ...]
is equivalent to .


gives a list of the parts , , ... of expr.


gives parts m through n.


gives parts m through n in steps of s.

DetailsDetails

  • You can make an assignment like to modify any part or sequence of parts in an expression. »
  • Part 0 of an expression is its head.
  • Common spans of parts include:
  • expr[[m;;]]part m through the end
    expr[[;;n]]from the beginning to part n
    expr[[;;,j]]column j
    expr[[m1;;n1,m2;;n2]]submatrix
  • When expr is a list, gives a list of parts. In general, the head of expr is applied to the list of parts. »
  • You can get a nested list of parts from . Each part has one index from each list.
  • If any of the are All or , all parts at that level are kept.
  • Notice that lists are used differently in Part than in functions like Extract, MapAt, and Position.
  • If expr is a SparseArray object, gives the parts in the corresponding ordinary array. »
  • In StandardForm and InputForm, can be input as .
  • and can be entered as Esc[[Esc and Esc]]Esc or \[LeftDoubleBracket] and \[RightDoubleBracket].
  • In StandardForm, can be input as or .

ExamplesExamplesopen allclose all

Basic Examples (10)Basic Examples (10)

Pick out a part of a list:

In[1]:=
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Pick out a sequence of parts:

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Pick out a part of a matrix:

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The second row of a matrix:

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The second column of a matrix:

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An element 2 from the end of a list:

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A list of parts:

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Reassign a part:

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In[3]:=
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Reassign a sequence of parts:

In[1]:=
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In[2]:=
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In[3]:=
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Part works with expressions of any kind, not just lists:

In[1]:=
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In[2]:=
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In[3]:=
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Part always operates on the FullForm of expressions:

In[4]:=
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Out[4]=
In[5]:=
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Out[5]//FullForm=
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