# Lists

Lists can be entered in Mathics with curly braces { and }:

• mylist = {a, b, c, d}

There are various functions for constructing lists:

• Range[5]

• Array[f, 4]

• ConstantArray[x, 4]

• Table[n ^ 2, {n, 2, 5}]

The number of elements of a list can be determined with Length:

• Length[mylist]

Elements can be extracted using double square braces:

• mylist[[3]]

Negative indices count from the end:

• mylist[[-3]]

Lists can be nested:

• mymatrix = {{1, 2}, {3, 4}, {5, 6}};

There are alternate forms to display lists:

• TableForm[mymatrix]

• MatrixForm[mymatrix]

There are various ways of extracting elements from a list:

• mymatrix[[2, 1]]

• mymatrix[[;;, 2]]

• Take[mylist, 3]

• Take[mylist, -2]

• Drop[mylist, 2]

• First[mymatrix]

• Last[mylist]

• Most[mylist]

• Rest[mylist]

Lists can be used to assign values to multiple variables at once:

• {a, b} = {1, 2};

• a

• b

Many operations, like addition and multiplication, “thread” over lists, i.e. lists are combined element-wise:

• {1, 2, 3} + {4, 5, 6}

• {1, 2, 3} * {4, 5, 6}

It is an error to combine lists with unequal lengths:

• {1, 2} + {4, 5, 6}