Convert array of strings to array of integers

Question

How do I convert types in J?

For example, how to I convert an array of strings like "4" "78" "0" "_1" to an array of numbers like 4 78 0 _1

Answer 1

Note that what you call a string is, in fact, a byte list, so a string array is just a byte array of higher dimension.

There is a J primitive to interpret a byte array as a number, which is number (dyadic ".). It's dyadic because you also have to provide a default value in case a string cannot be interpreted as a number, or if some padding has to be done.

The usage is very simple: __".'2 -3 4e 5.6 _ .7' gives 2 _3 __ 5.6 _ 0.7 (see the documentation). As per the note, this generalizes to higher dimension arrays:

    __".'2 -3 4e 5.6 _ .7',:'1 7 9 2 4 1'
2 _3 __ 5.6 _ 0.7
1  7  9   2 4   1