# How to split a matrix columnwise and save each part as a matrix_part_i.txt file using a loop?

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Emerson De Souza on 8 May 2011
I want to split a matrix column-wise and
save each part with correct index.
The begin and end of each part is determined by a
parameter p as coded below:
clear;
X=rand(5,10); %Let M be a matrix with 10 columns
NUMBER_OF_OUTPUT_PARTS=2; %Let 2 be the amount of parts of a matrix
TOTAL_NUMBER_OF_COLUMNS=size(X,2);
NUMBER_OF_COLUMNS_PER_PART=TOTAL_NUMBER_OF_COLUMNS/NUMBER_OF_OUTPUT_P
ARTS;
for p=1:NUMBER_OF_OUTPUT_PARTS;
Xp{p}=X(:,
((p-1)*NUMBER_OF_COLUMNS_PER_PART)+1:NUMBER_OF_COLUMNS_PER_PART*p);
%Partition of main matrix into 2 parts
end;
%Output is two matrices each with 5 columns, as expected!!!
Since A=Xp{1,1} gives the first part
and B=Mp{1,2} the second part and so on,
I thought that I could automatically save all parts within the same
code by writing the following lines within the loop:
Xp{p}=X(:,
((p-1)*NUMBER_OF_COLUMNS_PER_PART)+1:NUMBER_OF_COLUMNS_PER_PART*p);
fid = fopen('Xp{p}.txt', 'wt');
fprintf(fid, [repmat('%g\t', 1, size(Xp{p},2)-1) '%g\n'], Xp{p}.');
fclose(fid);
Unfortunately it did not work.
So I wounder if someone knows what I should do to extract each part
of main matrix and save automatically within the loop with the
correct index without overwriting.
Emerson
Oleg Komarov on 8 May 2011

Walter Roberson on 8 May 2011
You would probably find it easier to use mat2cell() to split the matrix.
fid = fopen('Xp{p}.txt', 'wt');
you are using the same output file name each time. Perhaps you want something like,
fid = fopen(sprintf('X_%d.txt',p),'wt');
Emerson De Souza on 8 May 2011
Thank you Walter,
your suggested line solved the problem.
Later I will try the advantages of using mat2cell() to split the matrix and compare with the current commands.
I wish you a nice weekend
Emerson

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