Vectorize IF statement

Question

I am trying to vectorize an if statement in Matlab and I am not sure how to do it. I want to assign a 'N' for positive values and 'S' for negative values. I want to avoid a for loop but here is my code:

LatDD = [23.0,12.3,-43.2,9.9,-40.7]; LatDir = ['' '' '' '' '']; if (LatDD < 0) LatDir = 'S' else LatDir = 'N' end

Obviously this fails to do what I want because it really only checks the first element of LatDD. I could easily do a for loop but I want it to be vectorized. I tried logical indexing but all that got me was another vector with zeroes or ones which I would have to check with a for loop anyway.

craigim · Accepted Answer · 2015-10-06 03:10:06Z

You can use logical indexing here, you just have to do it twice

LatDD = [23.0,12.3,-43.2,9.9,-40.7]; LatDir = ['' '' '' '' '']; LatDir(LatDD < 0) = 'S'; LatDir(LatDD >= 0) = 'N';

Since you have a binary choice here, you could even skip a step by prefilling LatDir with all 'N' and just changing the ones corresponding to negative LatDD values to 'S'

LatDD = [23.0,12.3,-43.2,9.9,-40.7]; LatDir = ['N' 'N' 'N' 'N' 'N']; LatDir(LatDD < 0) = 'S';

Divakar · Accepted Answer · 2015-10-06 10:20:10Z

Here's a one-liner -

char('S'*(LatDD<0) + 'N'*(~(LatDD<0)))

Sample run -

>> LatDD = [23.0,12.3,-43.2,9.9,-40.7]; >> LatDir = ['' '' '' '' '']; >> char('S'*(LatDD<0) + 'N'*(~(LatDD<0))) ans = NNSNS

This also works but it is confusing for beginners like me. Thanks for answering though. It helps me and others learn the tricks.

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