## 1.8.6 Adding, Removing and Modifying List Elements

 Prepend[list, element] add element at the beginning of list Append[list, element] add element at the end of list Insert[list, element, i] insert element at position i in list Insert[list, element, -i] insert at position i counting from the end of list Delete[list, i] delete the element at position i in list ReplacePart[list, new, i] replace the element at position i in list with new ReplacePart[list, new, {i, j}] replace list[[i, j]] with new

Functions for manipulating elements in explicit lists.
This gives a list with x prepended.
 In[1]:=  Prepend[{a, b, c}, x]
 Out[1]=
This inserts x so that it becomes element number 2.
 In[2]:=  Insert[{a, b, c}, x, 2]
 Out[2]=
This replaces the third element in the list with x.
 In[3]:=  ReplacePart[{a, b, c, d}, x, 3]
 Out[3]=
This replaces the element in a matrix.
 In[4]:=  ReplacePart[{{a, b}, {c, d}}, x, {1, 2}]
 Out[4]=

Functions like ReplacePart take explicit lists and give you new lists. Sometimes, however, you may want to modify a list "in place", without explicitly generating a new list.

 v = {, , ... } assign a variable to be a list v[[i]] = new assign a new value to the i element

Resetting list elements.
This defines v to be a list.
 In[5]:=  v = {a, b, c, d}
 Out[5]=
This sets the third element to be x.
 In[6]:=  v[[3]] = x
 Out[6]=
Now v has been changed.
 In[7]:=  v
 Out[7]=

 m[[i, j]] = new replace the element of a matrix m[[i]] = new replace the i row m[[All, i]] = new replace the i column

Resetting pieces of matrices.
This defines m to be a matrix.
 In[8]:=  m = {{a, b}, {c, d}}
 Out[8]=
This sets the first column of the matrix.
 In[9]:=  m[[All, 1]] = {x, y}; m
 Out[9]=
This sets every element in the first column to be 0.
 In[10]:=  m[[All, 1]] = 0; m
 Out[10]=

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