Tally
From NARS2000


R is an arbitrary array.  
Z is an integer scalar whose value is the number of items along the first coordinate of R. 
For example,
≢⍬ 0 ≢23 1 ≢,23 1 ≢2 3 4⍴5 6 2
This symbol was suggested by the language designers of Dyalog APL.