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1.8.6 Adding, Removing and Modifying List Elements
Functions for adding and deleting elements in lists.
This gives a list with x prepended.
In[1]:= Prepend[{a, b, c}, x]
Out[1]= 
This adds x at the end.
In[2]:= Append[{a, b, c}, x]
Out[2]= 
This inserts x so that it becomes element number 2.
In[3]:= Insert[{a, b, c}, x, 2]
Out[3]= 
Negative numbers count from the end of the list.
In[4]:= Insert[{a, b, c}, x, -2]
Out[4]= 
Delete removes an element from the list.
In[5]:= Delete[{a, b, c, d}, 3]
Out[5]= 
Modifying parts of lists.
This replaces the third element in the list with x.
In[6]:= ReplacePart[{a, b, c, d}, x, 3]
Out[6]= 
This replaces the first and fourth parts of the list. Notice the need for double lists in specifying multiple parts to replace.
In[7]:= ReplacePart[{a, b, c, d}, x, {{1}, {4}}]
Out[7]= 
Here is a  identity matrix.
In[8]:= IdentityMatrix[3]
Out[8]= 
This replaces the  component of the matrix by x.
In[9]:= ReplacePart[%, x, {2, 2}]
Out[9]= 
Padding lists.
This pads with zeros on the left to make a list of length 10.
In[10]:= PadLeft[{a, b, c}, 10]
Out[10]= 
This pads with copies of the sequence x, y.
In[11]:= PadLeft[{a, b, c}, 10, {x, y}]
Out[11]= 
This leaves a margin of 3 elements on the right.
In[12]:= PadLeft[{a, b, c}, 10, {x, y}, 3]
Out[12]= 
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