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How can I concatenate two or more arrays without using num2str?

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Adriano on 20 Feb 2017
Answered: Adriano on 21 Feb 2017
For example if I have two vertical arrays:
A = [1;2] B = [3;4]
I need this output:
C = [13; 24]
The problem is that my arrays have many rows, thus num2str is too slow. What can I do? Thanks!!!


Adam on 20 Feb 2017
I can't help but think of the joke of someone asking for directions to somewhere and being told 'Well, if I were you I wouldn't start from here'.
There may be better suggestions based on the wider context of the code than already having A and B defined.

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Accepted Answer

John D'Errico
John D'Errico on 20 Feb 2017
Edited: John D'Errico on 20 Feb 2017
The most obvious solution is to appreciate how a number is constructed in decimal form. So, rather than convert to characters, then concatenate, and then go back in to numeric form, simply use base 10.
C = 10*A + B;


Guillaume on 20 Feb 2017
And a generic version of that for integers of any (reasonable) magnitude:
C = A .* 10.^ceil(log10(B)) + B
John D'Errico
John D'Errico on 20 Feb 2017
True. I expect that whenever I see an example with one digit integers, the real problem is always more complex. :)
Walter Roberson
Walter Roberson on 20 Feb 2017
I would max(1,log10(max(abs(B))))
though the desired outcome is not clear for negative values.

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