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. | |
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Prepend[{a, b, c}, x]
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| This inserts x so that it becomes element number 2. | |
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Insert[{a, b, c}, x, 2]
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| This replaces the third element in the list with x. | |
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ReplacePart[{a, b, c, d}, x, 3]
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This replaces the  element in a  matrix. | |
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ReplacePart[{{a, b}, {c, d}}, x, {1, 2}]
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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. | |
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| This sets the third element to be x. | |
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| Now v has been changed. | |
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| 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}}
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| This sets the first column of the matrix. | |
In[9]:=
m[[All, 1]] = {x, y}; m
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| This sets every element in the first column to be 0. | |
In[10]:=
m[[All, 1]] = 0; m
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