first, last

first

First item of a list

first x    first[x]

Where x is a list or dictionary, returns its first item, else x.

Often used with Each to get the first item of each item of a list, or of each key in a dictionary.

q)first 1 2 3 4 5
1
q)first 42
42
q)RaggedArray:(1 2 3;4 5;6 7 8 9;0)
q)first each RaggedArray
1 4 6 0
q)RaggedDict:`a`b`c!(1 2;3 4 5;"hello")
q)first RaggedDict  / value of first key
1 2
q)first each RaggedDict
a| 1
b| 3
c| "h"

Returns the first row of a table.

q)\l sp.q
q)first sp
s  | `s$`s1
p  | `p$`p1
qty| 300

first is the dual to enlist.

q)a:10
q)a~first enlist 10
1b
q)a~first first enlist enlist 10
1b

first is an aggregate function.

last

Last item of a list

last x    last[x]

Where x is a list or dictionary, returns its last item; otherwise x.

q)last til 10
9
q)last `a`b`c!1 2 3
3
q)last 42
42

---

Selection