Read in array data into different sized Fortran arrays


Let's say I have a 5 x 5 array of floating points in a file array.txt:

1.0 1.1 0.0 0.0 0.0 1.2 1.3 1.4 0.0 0.0 0.0 1.5 1.6 1.7 0.0 0.0 0.0 1.8 1.9 1.0 0.0 0.0 0.0 1.1 1.2

I know this is probably a strange thing to do, but I'm just trying to learn the read statements better: I want to create two 3x3 arrays in Fortran, i.e. real, dimension(3,3) :: array1, array2 and try reading in the first 9 values by row into array1 and the following 9 values into array2. That is, I would like arrays to have the form

array1 = 1.0 1.1 0.0 0.0 0.0 1.2 1.3 1.4 0.0 array2 = 0.0 0.0 1.5 1.6 1.7 0.0 0.0 0.0 1.8

Next I want to try to do the same by columns:

array1 = 1.0 1.2 0.0 0.0 0.0 1.1 1.3 1.5 0.0 array2 = 0.0 0.0 1.4 1.6 1.8 0.0 0.0 0.0 1.7

My "closest" attempt for row-wise:

program scratch implicit none real, dimension(3,3) :: array1, array2 integer :: i open(12, file="array.txt") !read in values do i = 1,3 read(12,'(3F4.1)', advance="no") array1(i,:) end do end program scratch

My questions:

A. How to advance to next record when at the end?

B. How to do the same for reading in column-wise?

C. Why is '(3F4.1)' needed, as opposed to '(3F3.1)'?


Reading by line is easy :

READ(12,*) ((array1(i,j),j=1,3),i=1,3),((array2(i,j),j=1,3),i=1,3)

"advance='no'" is necessary only if you use 2 read statements instead of 1 (and only on the first READ). But this works only with explicit format ...

Reading a file by column is not so obvious, especially because reading a file is usually an expensive task. I suggest you read the file in a larger table and then you distribute the values into your two arrays. For instance :

real :: table(5,5) integer :: i,j,ii,jj,k .. read(12,*) ((table(i,j),j=1,5),i=1,5) k=0 do j=1,3 do i=1,3 k=k+1 jj=(k-1)/5+1 ii=k-(jj-1)*5 array1(i,j)=table(ii,jj) enddo enddo do j=1,3 do i=1,3 k=k+1 jj=(k-1)/5+1 ii=k-(jj-1)*5 array2(i,j)=table(ii,jj) enddo enddo

(3F4.1) is better than (3F3.1) because each number occupies 4 bytes in fact (3 for the digits and 1 for the space between numbers). But as you see, I have used * which avoids to think about such detail.


because of the requirement to "assign by columns" i would advise reading the whole works into a 5x5 array:

real tmp(5,5) read(unit,*)tmp

(note no format specification required)

Then do the assignments you need using array operations.

for this small array, the simplest thing to do seems to be:

real tmp(5,5),flat(25),array1(3,3),array2(3,3) read(unit,*)tmp flat=reshape(tmp,shape(flat)) array1=reshape(flat(:9),shape(array1)) array2=reshape(flat(10:18),shape(array2))

then the transposed version is simply:

flat=reshape(transpose(tmp),shape(flat)) array1=reshape(flat(:9),shape(array1)) array2=reshape(flat(10:18),shape(array2))

If it was a really big array I'd think of a way that avoided making an extra copy of the data.

Note you can wrap each of those assignments in transpose if needed depending on how you really want the data represented, eg.



  • perl - need to add set of lines into a file
  • array of string pointers in C
  • Swift Cast Generics Type
  • sort a array according to another array, swift
  • Determining signed state for HDF5 variables in NetCDF
  • Numpy “:” operator broadcasting issues
  • Is there a filesystem plugin available for django?
  • In C,why is definition of a global variable in a separate statement raising warning,but is OK for a
  • How can I create, read, update and delete Mediawiki articles via scripts?
  • Best style for iterating over a small number of items in Python?
  • ZeroMQ poll thread safety
  • How clojure map and keyword could be a function [duplicate]
  • Amazon S3 - 405 Method Not allowed using POST (Although I allowed POST on the bucket)
  • How to write .bin file in R and open it in Fortran
  • SCSS Language Injection in Pycharm
  • Configure WAF Application Gateway in front of App Services [closed]
  • How concerned should we be about thread safety with JSF managed beans?
  • Pytest/Allure - How to generate testcase description?
  • Type safe keys with Entity Framework model
  • Efficient User-Agent Regex to find Safari in Python
  • C# - Most efficient way to iterate through multiple arrays/list
  • Memory error in python- how to use more memory
  • Differences in dis-assembled C code of GCC and Borland?
  • Z3: Convert between FP and BitVector?
  • How does this usort cmp function actually work?
  • How can I extract results of aggregate queries in slick?
  • Date Conversion from yyyy-mm-dd to dd-mm-yyyy
  • Installed module is empty
  • Typescript - Unable to get 'import' statement to function
  • Reading JSON from a file using C++ REST SDK (Casablanca)
  • Algorithm for a smudge tool?
  • Using jQuery closest() method with class selector
  • QLineEdit password safety
  • Counter field in MS Access, how to generate?
  • Running a C# exe file
  • Convert array of 8 bytes to signed long in C++
  • How to disable jQuery.jplayer autoplay?
  • What are the advantages and disadvantages of reading an entire file into a single String as opposed
  • Checking variable from a different class in C#
  • Running Map reduces the dimensions of the matrices