It's trivial to extend the SERIES library to allow collecting sums in a hash-table (It was just a cut-paste of the collect-hash function with setf changed to in

It's trivial to extend the SERIES library to allow collecting sums in a hash-table (It was just a cut-paste of the collect-hash function with setf changed to incf; further extending to allow generic modifications of values is an exercise left to the reader). That allows a shorter (but not as short as I'd like) implementation. It could be shorter if the output list were to have elements like ("one" 1) as the multiple-value-bind exists to reverse that ordering for unpacking the hash-table at the end. Here's the result (if you wanted to further optimize and know that the result will fit in a fixnum (i.e. +/- 2^62 on modern implementations, you can change the "'number" to "'fixnum"): (defun unique-sum (list) (multiple-value-bind (keys values) (scan-hash (collect-hash-sum (map-fn 'string #'cadr (scan list)) (map-fn 'number #'car (scan list)) :test #'equal)) (map-fn 'list #'list values keys))) And the extension to SERIES: (series::defS collect-hash-sum (keys values &rest option-plist) "(collect-hash keys values :test :size :rehash-size :rehash-threshold) Combines a series of keys and a series of values together into a hash table. Duplicate keys sum the values. The keyword arguments specify the attributes of the hash table to be produced. They are used as arguments to MAKE-HASH-TABLE" (fragl ((keys t) (values t) (option-plist)) ((table)) ((table t (apply #'make-hash-table option-plist))) () () ((incf (gethash keys table 0) values)) () () nil) :optimizer (series::apply-literal-frag (list '(((keys t) (values t) (table)) ((table)) () () () ((incf (gethash keys table 0) values)) () () nil) keys values `(make-hash-table ,@ option-plist))) :trigger t)