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Cell conversion to double

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Steven il 17 Ott 2011
Commentato: Hiril Patel il 19 Giu 2022
Let's say a is a 11x1 cell like this
a =
and I want to convert it in double. If I try b=cell2mat(a), I got the following error :
??? Error using ==> cat
CAT arguments dimensions are not consistent.
Error in ==> cell2mat at 85
m{n} = cat(1,c{:,n});
However, I know I can bypass it with a loop with 2 conversion as:
for i = 1:length(a)
b(i) = str2num(cell2mat(a(i)));
Thus, I wonder if there is a simpler way to do this with an easy one-step function.
  3 Commenti
ayesha abbassi
ayesha abbassi il 24 Feb 2018
B = cell2mat(A). now check its type by writing whos B in command window
Chrysi K.
Chrysi K. il 5 Feb 2019
@ayesha abbassi Thank you so much!!! You helped me!!! I had a similar problem!

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Risposta accettata

Jan il 17 Ott 2011
Modificato: MathWorks Support Team il 8 Nov 2018
To convert a cell array of character vectors to numbers, you can use the str2double function. This function is the simplest method.
C = {'0.000000'; '10.000000'; '100000.000000'};
M = str2double(C)
The cell2mat function converts a cell array of character vectors to a character array, and only if all the character vectors have the same length. cell2mat also preserves the data type of the contents of the cells, so it does not convert characters to numbers.
If you need your code to be fast, then use the following code instead. This code is faster than str2double:
C = {'0.000000'; '1.000000'; '2.000000'; ...
'3.000000'; '4.000000'; '5.000000'; '6.000000'
'7.000000'; '8.000000'; '9.000000'; '10.000000'};
S = sprintf('%s*', C{:});
N = sscanf(S, '%f*');
Unfortunately sprintf seems to forget a proper pre-allocation. This C-Mex is 4 times faster: FEX: CStr2String:
S = CStr2String(C, '*');
N = sscanf(S, '%f*');
Timings in 2011b, Core2Duo:
n = 100;
C = cell(1, n);
for iC = 1:n; C{i} = sprintf('%f', i); end
tic; for i=1:1000; N = cellfun(@(x)str2double(x), C); end; toc
>> 3.61 sec
tic; for i=1:1000; N = cellfun(@(x) sscanf(x, '%f'), C); end; toc
>> 3.01 sec
tic; for i=1:1000; N = str2double(C); end; toc
>> 2.79 sec
tic; for i=1:1000; N = cellfun(@str2double, C); end; toc
>> 2.49 sec
tic; for i=1:1000;
N = zeros(1,100); for j=1:100; N(j) = sscanf(C{j}, '%f'); end;
end; toc
>> 1.40 sec
tic; for i=1:1000; N = sscanf(sprintf('%s*', C{:}), '%f*'); end; toc
>> 0.14 sec
tic; for i=1:1000; N = sscanf(CStr2String(C, '*'), '%f*'); end; toc
>> 0.071 sec
To my surprise a full implementation in C is slower than sscanf(sprintf()), see FEX: String to double. Matlab's sscanf seems to be much better than the MSVC implementation.
  9 Commenti
Giuseppe Degan Di Dieco
Giuseppe Degan Di Dieco il 28 Giu 2021
Dear Jan,
thanks for your tip. Still useful these days.
Hiril Patel
Hiril Patel il 19 Giu 2022
Hello Jan
i have cell of 73x1 of splitted data which i would like to convert to decimal but when I use M = str2double(adc_data). it returns to NaN
here is the string data i splitted

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Più risposte (1)

Daniel Shub
Daniel Shub il 17 Ott 2011
It appears your cell array contains strings and not numbers (doubles).
b = cellfun(@(x)str2double(x), a);
  6 Commenti
Fangjun Jiang
Fangjun Jiang il 17 Ott 2011
+1, For none-time-critical task, I still vote for using str2double().
hello_world il 4 Lug 2018
@Daniel Shub: It converts all cell entries (which are string) into NaN values. I have raised a question at:
Can you please look into that?

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