Cell conversion to double

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Steven el 17 de Oct. de 2011
Comentada: Hiril Patel el 19 de Jun. de 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 comentarios
ayesha abbassi
ayesha abbassi el 24 de Feb. de 2018
B = cell2mat(A). now check its type by writing whos B in command window
Chrysi K.
Chrysi K. el 5 de Feb. de 2019
@ayesha abbassi Thank you so much!!! You helped me!!! I had a similar problem!

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Respuesta aceptada

Jan el 17 de Oct. de 2011
Editada: MathWorks Support Team el 8 de Nov. de 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 comentarios
Giuseppe Degan Di Dieco
Giuseppe Degan Di Dieco el 28 de Jun. de 2021
Dear Jan,
thanks for your tip. Still useful these days.
Hiril Patel
Hiril Patel el 19 de Jun. de 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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Más respuestas (1)

Daniel Shub
Daniel Shub el 17 de Oct. de 2011
It appears your cell array contains strings and not numbers (doubles).
b = cellfun(@(x)str2double(x), a);
  6 comentarios
Fangjun Jiang
Fangjun Jiang el 17 de Oct. de 2011
+1, For none-time-critical task, I still vote for using str2double().
hello_world el 4 de Jul. de 2018
@Daniel Shub: It converts all cell entries (which are string) into NaN values. I have raised a question at: https://www.mathworks.com/matlabcentral/answers/408675-how-to-convert-a-csv-file-of-cell-array-type-to-double
Can you please look into that?

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