Q Language - Verb & Adverbs

Kdb+ has nouns, verbs, and adverbs. All data objects and functions are nouns. Verbs enhance the readabipty by reducing the number of square brackets and parentheses in expressions. Adverbs modify dyadic (2 arguments) functions and verbs to produce new, related verbs. The functions produced by adverbs are called derived functions or derived verbs.

Each

The adverb each, denoted by ( ` ), modifies dyadic functions and verbs to apply to the items of psts instead of the psts themselves. Take a look at the following example −

q)1, (2 3 5)       / Join
1 2 3 5

q)1,  ( 2 3 4)     / Join each
1 2
1 3
1 4

There is a form of Each for monadic functions that uses the keyword “each”. For example,

q)reverse ( 1 2 3; "abc")           /Reverse
a b c
1 2 3

q)each [reverse] (1 2 3; "abc")     /Reverse-Each
3 2 1
c b a

q) [reverse] ( 1 2 3; "abc")
3 2 1
c b a

Each-Left and Each-Right

There are two variants of Each for dyadic functions called Each-Left (:) and Each-Right (/:). The following example explains how to use them.

q)x: 9 18 27 36

q)y:10 20 30 40

q)x,y            / join
9 18 27 36 10 20 30 40

q)x, y           / each

9   10
18  20
27  30
36  40

q)x: 9 18 27 36

q)y:10 20 30 40

q)x,y            / join
9 18 27 36 10 20 30 40

q)x, y           / each, will return a pst of pairs

9   10
18  20
27  30
36  40

q)x, :y         / each left, returns a pst of each element
                 / from x with all of y
					  
9   10  20  30  40
18  10  20  30  40
27  10  20  30  40
36  10  20  30  40

q)x,/:y          / each right, returns a pst of all the x with
                 / each element of y
					  
9  18  27  36  10
9  18  27  36  20
9  18  27  36  30
9  18  27  36  40

q)1 _x           / drop the first element
18 27 36

q)-2_y           / drop the last two element
10 20

q)               / Combine each left and each right to be a
                 / cross-product (cartesian product)
                 
q)x,/::y

9   10  9   20  9   30  9   40
18  10  18  20  18  30  18  40
27  10  27  20  27  30  27  40
36  10  36  20  36  30  36  40