List Difference Functions

See also List Union, List Intersection & List Symmetric Difference

Difference of Two Lists

 Function Syntax (LM:ListDifference ) Current Version 1.0
Arguments
Symbol Type Description
l1,l2 List Lists for which to return the Difference
Returns
Type Description
List List of items appearing exclusively in list l1

Program Description

This subfunction will return a list expressing the difference or relative complement of two lists, that is, a list of items appearing exclusively in one list but not another.

Recursive Version

Select all
```;;-------------------=={ List Difference }==------------------;;
;;                                                            ;;
;;  Returns items appearing exclusively in one list but not   ;;
;;  another, i.e. the relative complement: l1 \ l2            ;;
;;------------------------------------------------------------;;
;;  Author: Lee Mac, Copyright © 2011 - www.lee-mac.com       ;;
;;------------------------------------------------------------;;
;;  Arguments:                                                ;;
;;  l1,l2 - lists for which to return the difference          ;;
;;------------------------------------------------------------;;
;;  Returns:  List of items appearing exclusively in list l1  ;;
;;------------------------------------------------------------;;

(defun LM:ListDifference ( l1 l2 )
(if l1
(if (member (car l1) l2)
(LM:ListDifference (cdr l1) l2)
(cons (car l1) (LM:ListDifference (cdr l1) l2))
)
)
)
```

Iterative Version

Select all
```;;-------------------=={ List Difference }==------------------;;
;;                                                            ;;
;;  Returns items appearing exclusively in one list but not   ;;
;;  another, i.e. the relative complement: l1 \ l2            ;;
;;------------------------------------------------------------;;
;;  Author: Lee Mac, Copyright © 2011 - www.lee-mac.com       ;;
;;------------------------------------------------------------;;
;;  Arguments:                                                ;;
;;  l1,l2 - lists for which to return the difference          ;;
;;------------------------------------------------------------;;
;;  Returns:  List of items appearing exclusively in list l1  ;;
;;------------------------------------------------------------;;

(defun LM:ListDifference ( l1 l2 )
(vl-remove-if '(lambda ( x ) (member x l2)) l1)
)
```

Example Function Call

```_\$ (LM:ListDifference '(1 2 3 4 5) '(2 4 6))
(1 3 5)
```

Difference of a Set of Lists

 Function Syntax (LM:ListsDifference ) Current Version 1.0
Arguments
Symbol Type Description
l1 List List from which items are to be subtracted
ls List List of lists whose items may be subtracted from l1
Returns
Type Description
List List of items appearing exclusively in list l1

Program Description

This subfunction will return a list expressing the difference or relative complement of a list with a set of lists, that is, a list of items appearing exclusively in one list but not any other.

Recursive Version

Select all
```;;-------------------=={ Lists Difference }==-----------------;;
;;                                                            ;;
;;  Returns items appearing exclusively in one list but not   ;;
;;  others, i.e. the relative complement: l1\l2\l3\...\lN     ;;
;;------------------------------------------------------------;;
;;  Author: Lee Mac, Copyright © 2011 - www.lee-mac.com       ;;
;;------------------------------------------------------------;;
;;  Arguments:                                                ;;
;;  l1 - list from which items are to be subtracted           ;;
;;  ls - list of lists whose items may be subtracted from l1  ;;
;;------------------------------------------------------------;;
;;  Returns:  List of items appearing exclusively in list l1  ;;
;;------------------------------------------------------------;;

(defun LM:ListsDifference ( l1 ls )
(if l1
(if (vl-some '(lambda ( l ) (member (car l1) l)) ls)
(LM:ListsDifference (cdr l1) ls)
(cons (car l1) (LM:ListsDifference (cdr l1) ls))
)
)
)
```

Iterative Version

Select all
```;;-------------------=={ Lists Difference }==-----------------;;
;;                                                            ;;
;;  Returns items appearing exclusively in one list but not   ;;
;;  others, i.e. the relative complement: l1\l2\l3\...\lN     ;;
;;------------------------------------------------------------;;
;;  Author: Lee Mac, Copyright © 2011 - www.lee-mac.com       ;;
;;------------------------------------------------------------;;
;;  Arguments:                                                ;;
;;  l1 - list from which items are to be subtracted           ;;
;;  ls - list of lists whose items may be subtracted from l1  ;;
;;------------------------------------------------------------;;
;;  Returns:  List of items appearing exclusively in list l1  ;;
;;------------------------------------------------------------;;

(defun LM:ListsDifference ( l1 ls )
(vl-remove-if '(lambda  ( x ) (vl-some '(lambda ( l ) (member x l)) ls)) l1)
)
```

Version Derived from Set Operations

Requires Lists Union & List Difference subfunctions

Select all
```(defun LM:ListsDifference ( l1 ls )
(LM:ListDifference l1 (LM:ListsUnion ls))
)
```

Example Function Call

```_\$ (LM:ListsDifference '(1 2 3 4 5 6 7 8 9) '((2 4 6) (1 2 3 5 8)))
(7 9)
```

See also List Union, List Intersection & List Symmetric Difference

textsize