Perlseeker_1 has asked for the wisdom of the Perl Monks concerning the following question:

Hi Experts,

i am trying to read a data from bunch of large files based on key element exist in another file

for example i have a file called file - 1 which has two fields name and number as below

file - 1 

K    1
J    2
L    3
H    4

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Bunch of large files contains data as below, i have mentioned only one file, we may have n number of files

file 01
K    01    JK    1234
J    02    HJ    5678
L    03    JH    6789
H    04    IH    5467

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i am reading all the files and will store it in an array called @filelist

@filelist
---------
file 01
file 02
file 03
file 04
file 05
file 06

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i am reading each element from the file - 1 and will see if it exists in any of the files avialable in @filelist if exists i need to print the value of that element to text file

for example when i read a file - 1 , the first element is K, take the K and seacrh if it exists in any of the files available in @filelist, for example the value of K is available in file 01, print the K 01 JK 1234 to some text file called output.txt

My code

my @array;

open F, "$input_file" or die "Couldn't Open File: $!";
while (<F>) {
chomp;
( my ( $name, $num ) = split /    /, $_ ) ;
push (@array, $name);
}
    
foreach my $name (@array) {

}

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Can anybody please help me on syntac

Replies are listed 'Best First'.
Re: how to check if a particular value exist in list of files stored in an array
by baxy77bax (Deacon) on Oct 29, 2013 at 10:41 UTC
    well here is a quick solution: but be aware there is more then one way to do it : 
    use strict;

@filelist = ("f1");

while(<DATA>){
  chomp;
  /^([^\t]*)\t/; # I assume it is tab seperated
  my $rec = $1;
  foreach my $file(@filelist){
    my $entry = qx(grep -P "^$rec\t" $file);# I assume it is tab seper
+ated
    print "$rec\t$file\t$entry";
  }
}


__DATA__
K    1
J    2
L    3
H    4

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    The cosde is a bit redundant but i'll leave it up to you to clean it up. You can simply redirect the putput to a third file with "perl program.pl > output" or use : 
    open (OUT, ">", $myoutfile) || die "$!"

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    cheers

    baxy

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[d/l]
[select]
Re: how to check if a particular value exist in list of files stored in an array
by hdb (Monsignor) on Oct 29, 2013 at 11:36 UTC

    Your approach is one good way to do it if you do a few minor modifications. Read your first file into a hash instead of an array for easier lookup: 

    my %records;
open my $fh, "<", $file1;
/^(\S+)\s/ and $records{$1}=1 while <$fh>;
close $fh;

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    I am using a regular expression to find the first column in your file which seems to be simpler here and can also be used as a test. For example, empty lines will be skipped automatically this way.

    Then open each of your other files in turn and check whether a given line shall be printed by doing a lookup in the hash: 

    for my $file (@filelist) {
    open my $fh01, "<", $file;
    /^(\S+)\s/ and defined $records{$1} and print while <$fh01>;
    close $fh01;
}

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    I have skipped all checks whether files can be opened etc. You need to add those yourself.

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[d/l]
[select]
      hdb,
      Defensive programming aside, I believe that this may not completely satisfy the requirements. Perlseeker_1 wasn't clear if value should be printed once for each time it appeared in the files, if it could appear more than once, etc. I could see it being one of at least 3 choices:
      • Print once for each instance in the big files
      • Print once per big file if it appears (can still be multipl)
      • Print exactly once if it appears in any of the big files
      Assuming option 3, short-circuiting would speed things up assuming the real world case wasn't also the worst case.

      Cheers - L~R

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        Agree. But I hope that my proposal will help as a starting point even if it does not meet all the requirements.

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