extracting particular row and column

I have a matrix like this

1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
5 6 7 8
5 6 7 8
5 6 7 8
5 6 7 8
9 10 11 12
9 10 11 12
9 10 11 12
9 10 11 12

like that so many rows.I want to extract every 4 row and 4 column continuously for whole row and save it in excel file.For a single row it works b=a(1:1:4),:);but for all row how can it possible.

Answer 1

[Guillaume]

Do you mean?

b = a(1:4:end, :)

[Tanmoyee Bhattacharya]

It will take every 4 th row.I want 1 to 4 row each time for 365 rows as I have 365 rows.

[Guillaume]

I really have no idea what you mean. Can you provide an example of the output you want?

b = a(1:4, :)

will give you row 1 to 4. I don't understand what "each time for 365 rows" mean.

[Tanmoyee Bhattacharya]

if true
  % code
endSir one file will contain 
1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
another file will contain 
5 6 7 8
5 6 7 8
5 6 7 8
5 6 7 8
third file will contain 
9 10 11 12
9 10 11 12
9 10 11 12
like that 365 files will be generated with 4 row and column. For every 4 th row one file will be created.

if true
  % code
end

[Guillaume]

I believe this is what you want:

assert(mod(size(a, 1), 4) == 0, 'number of rows is not a multiple of 4');
numcells = size(a, 1) / 4;  %number of matrices generated
b = mat2cell(a, ones(1, numcells)*4, size(a, 2)); %split a into matrices

%save as excel file however you want, e.g.:
savepath = 'C:\wherever\you want\to save your files\');
for bidx = 1:numcells
   xlswrite(fullfile(savepath, sprintf('%4d.xlsx', bidx)), b{bidx});
end

[Tanmoyee Bhattacharya]

Sir it is really fantastic.It works.

Answer 2

[Image Analyst]

Guillaume's first answer gave you every 4th row extracted from the original, and all columns will be included. Perhaps when you say you "want to extract every 4 row and 4 column" you want this:

m4 = m(1:4:end, 1:4:end);

or

m4 = imresize(m, 0.25, 'nearest');

This will subsample the matrix by 4 in both the row and column direction.