How to speed up this code?

Asked by pietro on 23 Jan 2019

Latest activity Answered by pietro on 24 Jan 2019

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Hi all,

I have the following code that I need to speed-up:

a(1).a='a';
a(2).a='b';
a(3).a='b';
a(4).a='c';
output=(contains(cellstr(char(a.a),'b')))

the desidered output is:

output=[0 1 1 0]

In my case the size of a is [11'000x1], so the computation is pretty slow.

How can I speed up the code?

Thanks

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Products

MATLAB

Release

R2017b

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Answer by Guillaume on 23 Jan 2019

Accepted Answer

Your code would be much faster if you didn't so many unnecessary conversions. a.a is a comma separated list (which is bascially a cell array) which you convert to a char array and then split back into a cell array.

output = contains({a.a}, 'b')

does the same without any conversion.

It's not clear from your simple example if you really want to use contains (which check that 'b' is present anywhere within the char vector) or strcmp (which check that the char vector is exactly identical to 'b') which would be faster or even == which would be even faster but only work if all char vectors are just one character.

output = strcmp({a.a}, 'b')  %faster than contains if whole string comparison is required

Other than that, there's not much option to speed this up.

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Answer by pietro on 24 Jan 2019

Thanks for the aswer. Now the code is really fast. I have to use contains, because I have to search for string patterns.

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