in reply to Re: Creating a Hash using only one column in an imported data file
in thread Creating a Hash using only one column in an imported data file

Thank you very much!! This was very helpful information. However, my data file is way too large to be able to use inside the code. I tried running it with the format below, and i'm getting 0 values are greater than x for all of the elements. Is there something wrong with the way i'm opening the file? 

 open (IN, "<$ARGV[0]") || die ("Cannot open $ARGV[0]: $!");
@MyData = <IN>;
use strict; use warnings; use feature 'say';

my @col9 = map {(split)[8]} <IN>;

foreach my $test (2,3,4,5,6,7,8,9) {
    my $count =scalar grep {$_ >= $test} @col9;
    say sprintf "%d values were >= %d", $count, $test;
}

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Re^3: Creating a Hash using only one column in an imported data file
by 1nickt (Canon) on Feb 13, 2017 at 21:27 UTC

    Hi Koda1234,

    The preferred (because it's safest ) way to open a file is the "three-argument form" (see open [suggestion: as a beginner, read the docs for the various functions; don't just copy examples you may see in the wild ]).

    Also:

    • Check that you got any input before using it.
    • $! will report the cause of open die-ing, but you can make your own check of the file so you can use your own error message.
    • Use while to read from your filehandle one line at a time, so even if it's big it won't fill your memory.
    • Use chomp to trim the newline character off the end of the line. Doesn't matter in your example, but it will soon enough...
    • Declare your array outside the while loop and use push to add the values to it as you split the lines. 
    use strict; use warnings; use feature 'say';

my $filename = $ARGV[0] or die "You must supply a filename";
-f $filename or die "You must supply the name of a file that exists!";

open my $IN, '<', $filename or die "Can't open < $filename: $!";

my @col9;

while ( my $line = <$IN> ) {
    chomp $line;
    push @col9, (split / /, $line)[8];
}

close $IN or die "Can't close $filename: $!";

foreach my $test ( 1, 9, 42, 666 ) {
    my $count = scalar grep { $_ >= $test } @col9;
    say sprintf "%d values were >= %d", $count, $test;
}

__END__

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    Hope this helps!


    The way forward always starts with a minimal test.
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      Thank you again. I will have to get used to manipulating data sets. Also, when trying to run your code, I am getting a syntax error around say sprintf, although it it looks identical to the one before.

[reply]

        I suppose you are copy/pasting and forgot use feature 'say'; ? Is that what the error tells you, or does it tell you something else?


        The way forward always starts with a minimal test.
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