CODEWITHSUNDEEP
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drumGod31
drumGod31

Reputation: 51

Nested For Loop Equivalent using "Each" Statement in Q

I am learning the Q programming language because my new job will require it. I am doing some practice exercises and am wondering whether it is possible to imitate a nested loop using the "each" keyword.

For example, I know that:

f:{x*x}
a:(1;2;3;4;5)
f each a -> 1 4 9 16 25j

However, lets say for instance that I want to imitate a nested for loop to multiply the values of two lists. If we have:

a:(1;2;3;4;5)
b:(1;2;3;4;5)

In conventional java, this would be done by:

for(int i = 0; i < a.length; i++) {
    for(int j = 0; j < b.length; j++) {
        System.out.println(a[i]*b[j]);
    }
}

Is it possible to imitate this nested for loop structure using "each" in q?

Upvotes: 0

Views: 606

Answers (1)

SeanHehir
SeanHehir

Reputation: 1593

You can achieve this using iterators (formerly adverbs) in kdb EG

a*/:b // Each Right

Will multiply each element of b by every element of a. In this case it would be as if you were iterating through b in your outer loop and a in your inner loop.

You could flip this to

a*\:b // Each Left

Which would have a in your outer loop and b in your inner loop. If a and b are the same length and you would like to multiply element-wise then you can do a simple

a*b

For more on iterators: https://code.kx.com/q/wp/iterators/

Upvotes: 3

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