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[Srabon]

The following codes produce a data-table containing 10x10 values.

[JohnCampbell]

This example has a few style changes you may find useful:

[Srabon]

(Thanks John. I just realized that my question was not clear enough and the problem was badly defined. Sorry about that. I am trying to restate the problem here.)

Say, I have a matrix stored in an external file as shown in data-table 1. (1) How can read this file? (2) Write a code that would generate a new matrix from data-table 1 to have data-table 2?

data-table 1 (given):

1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9

data-table 2 (to generate):

1 2 3 4 5
3 4 5 6 7
5 6 7 8 9


Many thanks!

[Srabon]

(1) To read this file I can declare x1,x2,x3 and so on. But this does not look efficient if there are thousands of columns. Can anyone suggest a better way?
Thanks!

[JohnCampbell]

You have a number of tasks to perform
-open the file
-determine the dimension of the array
-read the data
-create the new array
-write the new array

When reading the data and determining it's size, this is an area to consider how reliable the data is.
Do you need to do any checking of the data or test for read errors ?
What is the expected layout of the data ?

If your array is dimension n, it is reasonably easy with allocatable arrays to define the new array.

m = (n+1)/2
allocate (old(n,n))
allocate (new(n,m))
!
do j = 1,n,2
new(:,(j+1)/2) = old(:,j)
end do

or more simply, without need for a second array
do j = 1,n,2
write (100, fmt=...) old(:,j)
end do

Something to work on.