 |
Part
expr
[[
i
]] or Part[
expr
,
i
] gives the i
 part of expr.
expr
[[-
i
]] counts from the end.
expr
[[0]] gives the head of expr.
expr
[[
i
,
j
, ... ]] or Part[
expr
,
i
,
j
, ... ] is equivalent to expr
[[
i
]]
[[
j
]] ... .
expr
[[
,
, ... 
]] gives a list of the parts  ,  , ... of expr.
You can make an assignment like t
[[
i
]]
=
value to modify part of an expression.
When expr is a list, expr
[[
,
, ... 
]] gives a list of parts. In general, the head of expr is applied to the list of parts.
You can get a nested listing of parts from expr
[[
,
, ... ]]. Each part has one index from each list.
Notice that lists are used differently in Part than in functions like Extract, MapAt and Position.
expr
[[
Range[
i
,
j
]
]] can be used to extract sequences of parts.
In StandardForm and InputForm, expr
[[
spec
]] can be input as expr spec .
and can be entered as  [[ and ]] or \[LeftDoubleBracket] and \[RightDoubleBracket].
See the Mathematica book: Section 1.2.4, Section 1.2.4, Section 1.4.6, Section 1.8.4, Section 1.8.4, Section 2.1.4.
See also: First, Head, Last, Extract, Position, ReplacePart, MapAt, Take.
Related package: LinearAlgebra`MatrixManipulation`.
Further Examples
This extracts the third element from the list.
In[1]:= 
Out[1]= 
This extracts a list of elements.
In[2]:= 
Out[2]= 
The second input resets the third element of the list.
In[3]:= 
Out[3]= 
In[4]:= 
Out[4]= 
In[5]:= 
Out[5]= 
In[6]:= 
This picks out parts 2 and 4 of the sum, leaving their sum.
In[7]:= 
Out[7]= 
THIS IS DOCUMENTATION FOR AN OBSOLETE PRODUCT. SEE THE DOCUMENTATION CENTER FOR THE LATEST INFORMATION. | | | |
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