K Isn't Lisp (2004)(nsl.com)

  (frequencies (map second v))
  ;; => {"one" 2, "two" 2, "three" 1, "four" 1}

  ;; or:

  (update-vals (group-by second v) count)
  ;; => {"one" 2, "two" 2, "three" 1, "four" 1}

  ;; +(#:'=v[;1];?v[;1])
  ;; flip(count each group v[;1];unique v[;1])

  (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)))

  (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)

  (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)))

  v:((1;"one");(1;"two");(1;"three");(1;"one");(1;"four");(1;"two"))
  +(#:'=v[;1];?v[;1])

  echo '1 "one"\n1 "two"\n1 "three"\n1 "one"\n1 "four"\n1 "two"' | awk '{ counters[$2] += $1 } END { for (id in counters) { print counters[id], id } }'

  2 "two"
  1 "four"
  1 "three"
  2 "one"