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Sort a cell array of char

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New
New on 4 Apr 2011
Hi,
I have a cell array of chars (some of the cells should be strings while other should be doubles). Now I am trying to sort several of the rows that should be doubles and I get, of course, a sort from the left of the number as : 1001, 112, 14.. Tried to convert to double with both writing sort(double(...)) and cellfun(@double, ...,'Uniformoutput', false) and it won't accept: 1) ??? Error using ==> double Conversion to double from cell is not possible." 2)??? Error using ==> sort Input argument must be a cell array of strings. What can I do to get 14, 112, 1001... Thank you Keren

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Accepted Answer

Jan
Jan on 4 Apr 2011
The question is not clear. This is a contradiction:
1. "cell array of chars" 2. "(some of the cells should be strings while other should be doubles)"
From the later text I guess, you want to sort a cell vector which contains scalar doubles:
C = {1001, 112, 14};
[dummy, index] = sort([C{:}]);
sortedC = C(index);
CELLFUN(@double, ...) converts each element of the cell to a DOUBLE - therefore it does no change anything here!
 
EDITED: Now a method to sort a cell string according to the numbers the strings represent:
C = {'1001', '112', '14'};
Str = sprintf('%s,', C{:});
D = sscanf(Str, '%g,');
[dummy, index] = sort(D);
sortedC = C(index);

  3 Comments

New
New on 4 Apr 2011
I wasn't clear.
I have a cell array (5000 X 150 cell). Each cell is a char. Whether I have strings or numbers in this cell array they are defined as chars.
As I want to sort only the rows in which I have numbers I tried to convert those to doubles.
Is this explanation better?
Jan
Jan on 4 Apr 2011
Does the above added sorting method help?
New
New on 4 Apr 2011
Yes! Thank you! I would never think of doing something like this.
There is no direct way to sort such cell array?
Anyway, thank you very much.

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More Answers (1)

Teja Muppirala
Teja Muppirala on 4 Apr 2011
Instead of just "double" you should use "str2double". I'm pretty sure that does what you want.
A = {'1001', '112', '14'}
B = str2double(A)
[Bsorted,ordering] = sort(B)

  3 Comments

Jan
Jan on 4 Apr 2011
Correct, but the SSCANF(SPRINTF('%g,', C{:}), '%g,') approach is much faster than STR2DOUBLE for a {1 x 5000} cell (Matlab 2009a):
C = cell(1, 5000);
for i=1:5000; C{i}=sprintf('%.0f', rand*1000); end
tic; d = str2double(C); toc % 0.20 sec
tic; e = sscanf(sprintf('%g,', C{:}), '%g,'); toc % 0.01 sec
Teja Muppirala
Teja Muppirala on 4 Apr 2011
Wow, that's pretty slick! I wouldn't have thought of that.
Jan
Jan on 4 Apr 2011
And SPRINTF still wastes time, because it does not pre-allocate the output. Therefore using http://www.mathworks.com/matlabcentral/fileexchange/26077-cstr2string will make it twice as fast:
tic; e = sscanf(CStr2String(C, ','), '%g,'); toc % 0.005 sec

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