tally

It produces an hash table (multiset) y which tallies the frequencies of occurrences of items in the list x, i.e., y_i is the number of times i appears in x, or is 0 if i doesn't appear in the list.

     i1 = y = tally {1,2,3,a,b,1,2,a,1,2,{a,b},{a,b},a}
     
     o1 = tally {2 : {a,b}, 3 : a, 1 : b, 3 : 1, 3 : 2, 1 : 3}
     
     o1 : Tally
     

     i2 = y_{a,b}
     
     o2 = 2
     

See also Tally.

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