Question

I have a huge set of data in Excel file sheet 1. The number of columns is fixed (6) but there are lots of rows.

For every 3 rows, I need to pick out the minimum value of 2nd column and save the whole row into Excel file or sheet 2, how am I going to write the script?

item.xls (sheet 1):

0.3 0.5 0.1 0.8 0.4 0.6
0.2 0.4 0.9 0.1 0.9 0.4
0.2 0.3 0.1 0.01 0.2 0.5
0.3 0.5 0.1 0.8 0.01 0.2
0.2 0.2 0.9 0.1 0.2 0.4
0.2 0.3 0.1 0.01 0.3 0.5
.......

In the first 3 rows, the minimum value of 2nd column is 0.3, then write the whole row into sheet 2 of the Excel file.

Then the next 3 rows, the minimum value of 2nd column is 0.2, then write the whole row into sheet 2 of the Excel file.

The result I would like to get is:

item.xls (sheet2):

0.2 0.3 0.1 0.01    % 1st 3 rows, the minimum value is 0.3 in 2nd column
0.2 0.2 0.9 0.1     % 2nd set of 3 rows, the minimum value is 0.2 in 2nd column
...

Answer 1

I will show how to extract the relevant rows from the data in a vectorized manner. I will leave the part of reading/writing excel files to you (it should be straightforward):

%# sample data
data = rand(3*10,6);

%# for each three rows, find the min of second column, and get the row index
[r c] = size(data);
d = permute(reshape(data',[c 3 r/3]),[2 1 3]);  %'# split into third dimension
[~,idx] = min(d(:,2,:));                        %# find min of col2
idx = squeeze(idx) + (0:3:(r-1))';              %'# adjust indices

%# extract these rows from the data matrix
result = data(idx,:);