How to access substrings out of cell array with indexing?

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Osvald Ljungstrand 2016-12-20

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评论： Osvald Ljungstrand 2016-12-21

Hi all, I searched a lot through the community as there was normally someone with a similar problem. But this time I was not able to find a solution.

I have a cell array (over 13,000x1) with strings and need to extract the number within. Example:

message = {  'error(1): occured due to A'    ; ...
    'error(25): occured due to B'   ; ...
    'error(306): occured due to C' };

With 'regexp' I can identify the position of the number:

[a,e] = regexp(message,'\(\d*\)');

Normally I prefer logical indexing but couldn't find a nice solution to access the substrings within a cell array. So for this small array I can extract the number with a loop

number = zeros(size(message,1),1);
for i=1:size(message,1)
    number(i) = str2double(message{i}(a{i}+1:e{i}-1)); 
end

But the for-loop is very time consuming for big cell arrays. I would prefer to use the existing a and e array.

Does anyone has a better way to access substrings within cell arrays?

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Answer 1

Andrei Bobrov 2016-12-20

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message = {  'error(1): occured due to A'    ; ...
    'error(25): occured due to B'   ; ...
    'error(306): occured due to C' }
a = regexp(message,'\d+','match','once')
out = str2double(a)

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Answer 2

David Barry 2016-12-20

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If you are using R2016b then you can make use of the new String datatype and then use the extractBetween function. This should be very quick.

message = {  'error(1): occured due to A'    ; ...
'error(25): occured due to B'   ; ...
'error(306): occured due to C' };
message = string(message);
nums = extractBetween(message, '(', ')');
nums = str2double(nums);

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David Barry 2016-12-20

Or see Andrei's answer if you are using an older release.

Osvald Ljungstrand 2016-12-21

Nonehteless my "message" looks a bit more complex and I can't just copy paste your suggestion, the combination of the 'match' option for regexp with the extractBetween function will solve my problem perfectly. Thank you a lot for your help

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