tally(VisibleList) -- tally the elements of a list, sequence, or array

Synopsis

Function: tally
Usage:

y = tally x
Inputs:
- x, a visible list,
Outputs:
- y, a tally, a listing of tallied results

Description

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{{a, b} => 2}
           1 => 3
           2 => 3
           3 => 1
           a => 3
           b => 1

o1 : Tally

i2 : y_2

o2 = 3

i3 : y_5

o3 = 0

i4 : y_{a,b}

o4 = 2