Cumultative sum of a list of values

[jbreard]

Hello everyone,

 

Do anyone know how to calculate efficiently the cumulative sum list of a list of value without using a loop explicitly ?

 

Given a list of value (a b c d e...), I want to calculate the list (a (a+b) (a+b+c) (a+b+c+d)....). I'm sure there is a simple way to do such a thing with recursion but I can't quite understand yet how these particuliar functions work.

 

I searched the forum and I found approaching topics but nothing that I could understand enough to perform such a function.

 

Thanks a lot and have a great day,

 

Jacques

[Stefan BMR]

(defun _sums (l / s)
  (setq s 0)
  (mapcar '(lambda (x) (setq s (+ s x))) l)
)

 

_$ (_sums '(1 2 3 4))
(1 3 6 10)
_$ 

 

[jbreard]

It works like a charm ! Thanks so much Stefan

 

Now I will have to understand how it works so well.

 

Thanks again,

 

Jacques

[Lee Mac]

Another, for fun, recursive & inefficient -

(defun trinum ( l )
    (if (cdr l)
        (cons (car l) (trinum (cons (+ (car l) (cadr l)) (cddr l))))
        l
    )
)