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group

Syntax: group x, group[x]

Returns a dictionary in which the keys are the distinct items of x, and the values the indexes where the distinct items occur.

The order of the keys is the order in which they appear in x.

q)group "mississippi"
m| ,0
i| 1 4 7 10
s| 2 3 5 6
p| 8 9

To count the number of occurrences of each distinct item:

q)count each group "mississippi"
m| 1
i| 4
s| 4
p| 2

To get the index of the first occurrence of each distinct item:

q)first each group "mississippi"
m| 0
i| 1
s| 2
p| 8

ungroup, xgroup
Basics: Sorting