Combinations without repetition 3 and 4 element.

Please publish a function that creates combinations.

List of any length.

Example:

'(1 2 3 4 5)

The result for the 3-element subsets.

    '(1     2     3)
    (1     2     4)
    (1     2     5)
    (1     3     4)
    (1     3     5)
    (1     4     5)
    (2     3     4)
    (2     3     5)
    (2     4     5)
    (3     4     5)

The result for the 4-element subsets.

    '(1     2     3     4)
    (1     2     3     5)
    (1     2     4     5)
    (1     3     4     5)
    (2     3     4     5)

(defun nCr ( l r )
   (cond
       (   (< r 2)
           (mapcar 'list l)
       )
       (   l
           (append
               (mapcar '(lambda ( x ) (cons (car l) x)) (nCr (cdr l) (1- r)))
               (nCr (cdr l) r)
           )
       )
   )
)

_$ (ncr '(1 2 3 4 5) 3)
((1 2 3) (1 2 4) (1 2 5) (1 3 4) (1 3 5) (1 4 5) (2 3 4) (2 3 5) (2 4 5) (3 4 5))

Dear Lee Mac

How to find all combinations from list of numbers that have sum of each of combination below specific number.

For example :

1. List (1 2 3 4 5)

2. Maximum sum of each combination: 6

So the result is : ((1 5) (2 4) (1 2 3))

Thank you.

m4rdy

How to find all combinations from list of numbers that have sum of each of combination below specific number.

For example :

1. List (1 2 3 4 5)

2. Maximum sum of each combination: 6

 

So the result is : ((1 5) (2 4) (1 2 3))

See my post here.

Example:

_$ (lst< '(1 2 3 4 5) 7)
((1 2 3) (1 2) (1 3) (1 4) (1 5) (2 3) (2 4) (1) (2) (3) (4) (5))

Or, for equality:

(defun lst= ( l n )
   (vl-remove-if-not '(lambda ( x ) (= (sum x) n)) (combinations l))
)

_$ (lst= '(1 2 3 4 5) 6)
((1 2 3) (1 5) (2 4))

Dear Lee Mac,

Thank you.

m4rdy

You're most welcome - these are interesting functions to write.