These functions manipulate arrays and lists as sets.

**Synopsis**-
Extract the elements of a set that are not contained in other sets.

**Usage**-
`indices = complement (a, b, ..., c)`

**Description**-
This function computes the elements of the first argument (

`a`

) that are not contained in the sets given by the other arguments (`b,...,c`

) and returns them in the form of indices into the first argument. **Example**-

Upon return,a = {"foo", PI, 7}; b = [1,2,3,PI]; indices = complement (a, b);

`indices`

will have the value`[0, 2]`

since`a[0]`

and`a[2]`

are not contained in`b`

. **Notes**-
A set may either be an Array_Type or a List_Type object. For a homogeneous collection of objects, it is better to use an Array_Type. i.e.,

`[1,2,3]`

instead of`{1,2,3}`

. **See Also**-
`intersection, ismember, union, unique`

**Synopsis**-
Extract the common elements of two or more sets

**Usage**-
`indices = complement (a, b, ..., c)`

**Description**-
This function computes the common elements of two or more sets and returns them in the form of indices into the first argument.

**Example**-

Upon return,a = {"foo", 7, PI}; b = {PI, "bar", "foo"}; indices = intersection (a, b);

`indices`

will have the value`[0, 2]`

since`a[0]`

and`a[2]`

are the common elements of the sets. **Notes**-
A set may either be an Array_Type or a List_Type object. For a homogeneous collection of objects, it is better to use an Array_Type. i.e.,

`[1,2,3]`

instead of`{1,2,3}`

. **See Also**-
`complement, ismember, union, unique`

**Synopsis**-
test to see if the elements of one set are members of another

**Usage**-
`val = ismember (a, b)`

**Description**-
This function may be used to see which of the elements of the set

`a`

are members of the set`b`

. It returns a boolean array indicating whether or not the corresponding element of`a`

is a member of`b`

. **Notes**-
A set may either be an Array_Type or a List_Type object. For a homogeneous collection of objects, it is better to use an Array_Type. i.e.,

`[1,2,3]`

instead of`{1,2,3}`

. **See Also**-
`complement, intersection, union, unique`

**Synopsis**-
Form a set of the unique elements of one ore more subsets

**Usage**-
`abc = union (a, b,..., c)`

**Description**-
This function interprets each of its arguments as a set, then merges them together and returns only the unique elements. The returned value may either be an

`Array_Type`

or a`List_Type`

object. **Notes**-
`[1,2,3]`

instead of`{1,2,3}`

. **See Also**-
`complement, intersection, ismember, unique`

**Synopsis**-
Get the indices of the unique elements of a set

**Usage**-
`indices = unique (A)`

**Description**-
This function returns an array of the indices of the unique elements of a set.

**Notes**-
`[1,2,3]`

instead of`{1,2,3}`

. **See Also**-
`complement, intersection, ismember, union`

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