Cell conversion to double

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Steven
Steven 2011-10-17
评论： Walter Roberson 2024-12-13
Greetings, Let's say a is a 11x1 cell like this a = '0.000000' '1.000000' '2.000000' '3.000000' '4.000000' '5.000000' '6.000000' '7.000000' '8.000000' '9.000000' '10.000000' 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))); end Thus, I wonder if there is a simpler way to do this with an easy one-step function. Regards, Steven
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ayesha abbassi
ayesha abbassi 2018-2-24
B = cell2mat(A). now check its type by writing whos B in command window
Chrysi K.
Chrysi K. 2019-2-5
@ayesha abbassi Thank you so much!!! You helped me!!! I had a similar problem!

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Jan
Jan 2024-11-13
编辑：MathWorks Support Team 2024-11-13
此 个回答 已被 Walter Roberson 标记
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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: : 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 . Matlab's sscanf seems to be much better than the MSVC implementation.
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Christopher Saltonstall
Christopher Saltonstall 2024-12-12
编辑：Christopher Saltonstall 2024-12-13
@Jan I have a similar problem but a slightly different data set. My data set is read from a strangly formated .csv file an yields a table where each cell of the table has an array. When I read one cell of the table, I get something like this but much longer.
C = {'[0 1 2 3 4]'};
How can I convert this to a double array?
This is the only way that I have figured out how to do this but eval does not work with my data size.
A = cell2mat(C)
eval(['data = ' A])
Walter Roberson
Walter Roberson 2024-12-13
@Christopher Saltonstall
A = cellfun(@(S)str2num(S,Evaluation="restricted"), TableNameGoesHere.FieldNameGoesHere, 'uniform', 0)
possibly followed by a cell2mat(A) provided that all of the entries are the same size.

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Daniel Shub
Daniel Shub 2011-10-17
It appears your cell array contains strings and not numbers (doubles).
b = cellfun(@(x)str2double(x), a);
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Fangjun Jiang
Fangjun Jiang 2011-10-17
+1, For none-time-critical task, I still vote for using str2double().
hello_world
hello_world 2018-7-4
@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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