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Skip reading N real numbers while reading data from a ascii file

  1. Jul 4, 2012 #1
    Hi all,

    I'm upgrading a legacy f77 code to f90 standards. I'm trying to make some of the global arrays as dynamic arrays so that at a later stage it would be easier for me to parallelize whole application.
    Coming to my problem, I need to read some numbers from a text file so that I can allocate (just enough) memory to the multidimensional arrays. However, while reading the input text file I need to skip say 'n' real numbers and then resume reading. These real numbers span several records (=lines) in the input text file and the number of real numbers per record is not constant sad.
    In summary, I know how many real numbers I've to skip, but I do not know in how many records these numbers span.

    Code (Text):
    3 3 3
    1.23445 0.2345235 0.345234 0.123425235 0.12343245
    0.31415927 1.23445 0.2345235 0.345234 0.123425235 0.12343245
    0.31415927 1.23445 0.2345235
    0.31415927 1.23445 0.2345235 0.2345235
    0.123 0.3245 0.74565355 4.34623431 56.2352354
    0.31415927 1.23445 0.2345235 0.2345235
    I have to read first line and then skip 27 real numbers and then again start reading from line 7.
    I currently have a code which works but it is not efficient,
    My current code looks like this

    Code (Text):

    [COLOR="Blue"]Integer[/COLOR]:: i, j, k, ii, jj, kk, num
    [COLOR="Blue"]Real, Allocatable, Dimension[/COLOR](:,:,:):: x
    [COLOR="DimGray"]!Start reading the data from file, UNIT=16[/COLOR]
    [B]read[/B](16,*) i, j, k
    [COLOR="DimGray"]!I want to Skip reading data to dummy x(:,:,:) array[/COLOR]
    [B]read [/B](16,*) (((x(ii,jj,kk),ii=1,i),jj=1,j),kk=1,k)
    [COLOR="DimGray"]! Resume reading[/COLOR]
    [B]read[/B](16,*) num
  2. jcsd
  3. Jul 4, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    I would declare a dummy variable (e.g. SKIP) and then do
    READ ... I , J , K , (SKIP, IJK = 1 , I*J*K ) , .....

    In other words, read 27 numbers into the same variable, and then ignore it. That will handle the fact that you don't know how many numbers are on each line of the input file.

    Usually, the variables in an implied DO loop are array elements with subscripts, but they don't have to be.

    This trick can be useful for output as well, if you want to write N copies of the same value for some reason.
  4. Jul 5, 2012 #3
    dear AlephZero, thanks for your solution. I appreciate your help.
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