lisp,common-lisp , How would I get the min/max of a list using a key

## Question:

Tag: lisp,common-lisp

I currently have a list of objects, each containing a certain attribute. I would like to get the element of the list with the min attribute value. Is there a concise way of doing this?

The python equivalent would be something like: min(d, key=d.get)

Is there a way of getting the min/max N elements?

``````CL-USER 8 > (reduce #'min '((1) (-1) (3)) :key #'first)
-1
``````

or

``````CL-USER 9 > (loop for e in '((1) (-1) (3)) minimize (first e))
-1
``````

I fear getting the container element is more difficult:

``````CL-USER 9 > (defun minimum (list predicate key)
(when list
(let* ((m0 (first list))
(m1 (funcall key m0)))
(mapc (lambda (e0 &aux (e1 (funcall key e0)))
(when (funcall predicate e1 m1)
(psetf m0 e0 m1 e1)))
list)
m0)))
MINIMUM

CL-USER 10 > (minimum '((a 1) (b -1) (c -2)) #'< #'second)
(C -2)

CL-USER 11 > (minimum '((a 1) (b -1)) #'< #'second)
(B -1)

CL-USER 12 > (minimum '((a 1)) #'< #'second)
(A 1)

CL-USER 13 > (minimum '() #'< #'second)
NIL
``````

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