Cell conversion to double
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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
3 个评论
Barry Swindler
2016-5-30
编辑：Barry Swindler
2016-5-30
not sure if you found an answer yet, but a simple thing like this works.
m=zeros(size(a,1),size(a,2));
m=str2double(a);
still not just one step, but there's no need for a loop.
hope this helps!
ayesha abbassi
2018-2-24
B = cell2mat(A). now check its type by writing whos B in command window
Chrysi K.
2019-2-5
@ayesha abbassi Thank you so much!!! You helped me!!! I had a similar problem!
采纳的回答
Jan
2024-11-13
编辑：MathWorks Support Team
2024-11-13
35 个投票
此 个回答 已被 Walter Roberson
标记
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.
11 个评论
Daniel Shub
2011-10-17
Nice comparison. One of the benefits of my job is access to way more computational power than I need. In general, I rarely worry about efficiency, however a speed up of a factor of 50 is nothing to sneeze at.
Daniel Shub
2011-10-17
编辑：Jan
2025-12-13
A faster, although not necessarily viable way, is to have the cell array contain numbers and not strings. On my computer
for iC = 1:n; C{iC} = iC; end
tic; for i=1:1000; N = [C{:}]; end; toc
appears fastest, although not by as much as I would have guessed.
Fangjun Jiang
2011-10-17
+1, Nice work, Jan! str2double() has source code available. It uses sscanf().
@Daniel: Even [C{:}] seems to have problems with the pre-allocation. The C-Mex http://www.mathworks.com/matlabcentral/fileexchange/28916-cell2vec determines the needed output size at first. For the {1 x100} cell containing scalars it is 5 times faster than [C{:}] in 2001b.
Jan
2011-10-18
Inserted: N(j)=sscanf(C{j}, '%f').
hello_world
2018-7-4
编辑：Walter Roberson
2025-12-13
@Jan great example, but it does not help if the cell contains strings. I have raised a question with that problem at: https://www.mathworks.com/matlabcentral/answers/408675-how-to-convert-a-csv-file-of-cell-array-type-to-double
Can you please help with that?
Nishaban P.K.
2020-4-21
sir, I use str2double function ,it return some binary values like '00000111' into 111. why?
Giuseppe Degan Di Dieco
2021-6-28
Dear Jan,
thanks for your tip. Still useful these days.
Best.
Hiril Patel
2022-6-19
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
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
2024-12-13
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.
更多回答（1 个）
Daniel Shub
2011-10-17
It appears your cell array contains strings and not numbers (doubles).
b = cellfun(@(x)str2double(x), a);
6 个评论
Fangjun Jiang
2011-10-17
Believe it or not, you can use str2double directly.
a={'1','2'};
str2double(a)
Daniel Shub
2011-10-17
Wow, another reason to like str2double over str2num.
Jan
2011-10-17
cellfun(@str2double, C) is faster than str2double(C). Surprising!
Jan
2011-10-17
"cellfun(@str2double, C)" is faster than "str2double(C)". Surprising! But the indirection "cellfun(@(x)str2double(x), C)" wastes time.
Fangjun Jiang
2011-10-17
+1, For none-time-critical task, I still vote for using str2double().
hello_world
2018-7-4
编辑：Walter Roberson
2025-12-13
@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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