3 ms·

Doing the naive thing in CL without thinking about things like 'efficiency' or 'maintainability': (let ((test-input '((1 "one") (1 "two") (1 "three") (1 "one

by tmtvl 3y ago

Doing the naive thing in CL without thinking about things like 'efficiency' or 'maintainability': (let ((test-input '((1 "one") (1 "two") (1 "three") (1 "one") (1 "four") (1 "two")))) (mapcar (lambda (string) (list (count string test-input :test #'string= :key #'second) string)) (remove-duplicates (mapcar #'second test-input) :test #'string= :from-end t))) I will admit it's not as short as: v:((1;"one");(1;"two");(1;"three");(1;"one");(1;"four");(1;"two")) +(#:'=v[;1];?v[;1])

SeanLuke 3y ago
Now you have me thinking about how short I can make that. My revision: (defun doit (elts) (mapcar (lambda (elt) `(,(count elt elts :test 'equal :key 'second) ,elt)) (delete-duplicates (mapcar 'second elts) :test 'equal))))) or maybe (defun doit (elts) (loop for elt in (delete-duplicates (mapcar 'second elts) :test 'equal) collect `(,(count elt elts :test 'equal :key 'second) ,elt)))
- tmtvl 3y ago
  As much as Lisp isn't meant for code golf, I think the loop variation could be used as a (rather long) one-liner.
taeric 3y ago
My naive looked more like: (with apologies on likely messing up spacing in hn.) (let ((in '((1 "one") (1 "two") (1 "three") (1 "one") (1 "four") (1 "two")))) (loop with hash = (make-hash-table :test #'equal) for v in in do (incf (gethash (cadr v) hash 0)) finally (return (loop for key being the hash-keys of hash collect (list (gethash key hash) key)))))