Assembly of matrices using for loop

2018 8 31
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更新时间：2018 9 6
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I have 20 excel files containing matrix, each matrix has 49 columns (all the matrix has the same number of columns) and a variable number of lines (the number of lines is not always the same for all the matrix I have). I want to assemble all of them in one excel file , what makes a new matrix with 49 columns.This should not be addition but assembly. For exemple if I have these two matrix : A = [1 2;3 4] B = [5 6;7 8] The result I wish to have is a new matrix C while : C =
1 2
3 4
5 6
7 8
In other words it is sort of like joining the matrices but by adding each matrix to the previous one, successively from the line where the previous matrix has stopped while keeping the same number of columns (49).
Any idea how to do this? Thanks in advance

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madhan ravi
madhan ravi 2018-8-31
编辑：madhan ravi 2018-8-31
C=[A;B] this will give the result for the example?
Silver
Silver 2018-9-1
Thank you for answering.It does for this exemple, but for larger amounts of data, I need to use the For loop, and that's the problem.

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 采纳的回答

James Tursa
James Tursa 2018-8-31

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Read each individual file into a cell array element, then vertically concatenate the cells all at once.

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Silver
Silver 2018-9-1
Thank you James Tursa for answering. However I would like to know when you said "Read each individual file into a cell array element" Does this script work ?
for i=1:data_ver %data_ver is the nmber of line (size) of the matrix
for j=1:data_hor %data_hor is the nmber of columns(size) of the matrix
temp = cell2mat(cellstr(Data(i,j))) ; %fill matrix
A(i,j)=str2double(temp) ;
end
end
And what about "vertically concatenate the cells all at once" I dont see what that means. Thank you again.
Stephen23
Stephen23 2018-9-1
编辑：Stephen23 2018-9-1
@Silver: you do not need to use any loops, as MATLAB's file importing functions are quite capable of importing the entire file by themselves. Also importing the data as character and then using str2double is most likely a misdirection: MATLAB's file importing function already import numeric data as numeric. So none of your code is very useful, or a good way to approach this task. A much better approach is to read the documentation:
https://www.mathworks.com/help/matlab/standard-file-formats.html
and pick a suitable method for reading your files.
"And what about "vertically concatenate the cells all at once" I dont see what that means"
Once you have all of the imported numeric data into one cell array, after the loop you can vertically concatenate the imported data into one matrix, exactly as you requested, e.g.:
mat = vertcat(C{:})

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Stephen23
Stephen23 2018-9-1
编辑：Stephen23 2018-9-1

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Following the examples in the MATLAB documentation:
https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html
N = 20;
C = cell(1,N);
for k = 1:N
F = sprintf('file%d.txt', k);
C{k} = importdata(F);
end
out = vertcat(C{:})
Or use dir, as shown in the link I gave above.

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Silver
Silver 2018-9-1
Thank you so much @Stephen Cobeldick , I will try the code and follow the instructions in the documentation.
Silver
Silver 2018-9-3
编辑：Silver 2018-9-3
Thank you so much @Stephen Cobeldick, it really works!! Instead, am looking forward to export the structure into a excel file. Do you have any idea, cause am not realy skilful with structure. I tried this script, it didnt work:
writetable(struct2table(out), 'outputfile.xlsx') % out is the structure you put it in your comment.
Thanks in advance.
Stephen23
Stephen23 2018-9-4
编辑：Stephen23 2018-9-4
Inside the loop get the required data, e.g.:
N = 20;
C = cell(1,N);
for k = 1:N
F = sprintf('file%d.txt', k);
T = importdata(F);
C{k} = T.data;
end
out = vertcat(C{:})
Remember to accept the answer that helped you most to resolve your original question!
Silver
Silver 2018-9-4
It realy works!! Thank you so much :D , I apreciate your help that saves me x) !! Thank you again
Silver
Silver 2018-9-4
Am sorry for disturbing,but I have one last question @stephen Cobeldick >< : Actually in the program I added
G{k} = T.textdata;
And I want to extract data from T.textdata, but I want to take the first column starting from the second line till the end, like i mentionned in the photo below :
So when I write this code :
time = vertcat(G{:}{(2,:),1})
It does not work , and I get the error message "Expected one output from a curly brace or dot indexing expression, but there were 2 results." Should I for exemple put define the size of the T.textdata first ? Thanks again.
Stephen23
Stephen23 2018-9-5
编辑：Stephen23 2018-9-5
Extract the required data before putting it in C, something like this:
G{k} = T.textdata(2:end,1);
...
time = vertcat(G{:});
Here is an explanation of why your syntax does not work:
https://www.mathworks.com/matlabcentral/answers/329538-why-do-i-get-this-error-for-this-non-scalar-structure
Silver
Silver 2018-9-5
You rock !! Thank you so much it works, and thanks for explanation , appreciate that!
Silver
Silver 2018-9-6
It really helps me ! thank you again , For sure I've accepted the answer and flagged it ^^

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