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printing arrays

by Spooky (Beadle)
on Dec 31, 2008 at 14:16 UTC ( #733471=perlquestion: print w/ replies, xml ) Need Help??
Spooky has asked for the wisdom of the Perl Monks concerning the following question:

I have two arrays (@ID @name) that I wish to print out on a single line e.g., 123 Smith 456 Doe 789 Allen etc. (as you can see, there's a number followed by a nsame). I know in FORTRAN (yes, FORTRAN) you could use an implied loop but I'm sure how to do this in Perl. Any suggestions?

Comment on printing arrays
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Re: printing arrays
by borisz (Canon) on Dec 31, 2008 at 14:35 UTC
    There are several ways:
    use List::MoreUtils qw/mesh/; print join ' ', mesh @ID, @name;
    or
    # you lose the order and every id must be unique my %h; @h{@ID} = @name ; print join ' ', %h;
    or ...
    Boris
      Once you have the list that you want to print; you don't need to use a join join, instead you can just print it with $, set appropriately. $, is also known as $OFS and $OUTPUT_FIELD_SEPARATOR; use perldoc perlvar. This can be much more efficient even with small lists.
      my @arr = ( 1, "Ali", 2, "Bobbi", 3, "Charli" ); local $, = " "; print @arr, $/;
      Be well,
      rir

      Updated: join usage

      Updated: efficiency comment deleted.

        Using $, is just another way. But internally $, use join and is __not__ faster or more efficient as the join statement.
        Boris
      ..thanks so much!
Re: printing arrays
by Arunbear (Parson) on Dec 31, 2008 at 14:41 UTC

    Assuming there are as many ids as names:

    use strict; use warnings; my @ids = (123, 456, 789); my @names = qw(Smith Doe Allen); foreach my $i (0 .. $#ids) { print "$ids[$i] $names[$i]\n"; }

      You actually wouldn't want the \n on the end of

           print "$ids[$i] $names[$i]\n";

      That would only print one id/name combination per line, and (s)he wants the entire contents of both arrays on one line. Replace the \n with a space and it should work.

        ..thanks kdj - have a good new year's eve..
      ..thanks for the input - have a safe new year's eve!
Re: printing arrays
by johngg (Abbot) on Dec 31, 2008 at 16:15 UTC

    TIMTOWTDI again! You can use the default behaviour that separates array or list elements with a space in double-quoted strings. This construct, @{ [ ... ] }, allows you to interpolate bits of code inside double-quoted strings.

    $ perl -e ' @ids = qw{ 123 456 789 }; @names = qw{ ann joe flo }; print qq{@{ [ map qq{$ids[ $_ ] $names[ $_ ]}, 0 .. $#ids ] }\n};' 123 ann 456 joe 789 flo $

    I hope this is of interest.

    Cheers,

    JohnGG

Re: printing arrays
by swampyankee (Parson) on Dec 31, 2008 at 14:45 UTC

    Please, it's not FORTRAN any longer; it's Fortran.

    Fortran has better i/o and string handling than a lot of people seem willing to accept. However, even I, who remains a Fortran afficionado and partisan, will admit that Perl's are, on the whole, better. It's C that's made a mess its string handling routines (strcat, anyone?).


    Information about American English usage here and here. Floating point issues? Please read this before posting. — emc

      ...so sorry - my fault! ..have a safe new year's eve!
Re: printing arrays
by Perlbotics (Canon) on Dec 31, 2008 at 14:57 UTC

    TIMTOWTDI: Limits the output to the shortest sequence but comes at the cost of an implicite extra-array...

    use strict; use warnings; my @ID = qw(123 456 789 666); my @name = qw(Smith Doe Allen); my $line = join(' ', map { $ID[$_], $name[$_] } 0..($#ID < $#name ? $#ID : $#name) ); print "($line)\n"; #output: (123 Smith 456 Doe 789 Allen)
Re: printing arrays
by kyle (Abbot) on Dec 31, 2008 at 17:06 UTC

    If you don't mind destroying the arrays, you can do it this way.

    printf "%s %s\n", shift( @ID ), shift( @name ) while @ID && @name;

    My first thought, however, was the List::MoreUtils solution that borisz gave.

    Update with a slightly silly way:

    my @nyuck = ( @ID, reverse @name ); printf "%s %s\n", shift( @nyuck ), pop( @nyuck ) while @nyuck;
Re: printing arrays
by spx2 (Chaplain) on Dec 31, 2008 at 18:14 UTC
    You could use map and an additional counter like this
    @name = ("one","two","three"); @ID = (1,2,3); $i=0; print map{ ($_,$ID[$i++]); } @name;
    or maybe you can have a look at how interleave two arrays.
    of course someone has thought of a more general map operator , it's called mapcar :) (I found about it in the link above),it seems very handy

    happy new year ! :)
Re: printing arrays
by apl (Monsignor) on Dec 31, 2008 at 15:14 UTC
    I know in FORTRAN (yes, FORTRAN)
    -4, -10, -77 or -9X? (Fortran-4 was one of my first two languages...)
Re: printing arrays
by hda (Hermit) on Jan 01, 2009 at 14:19 UTC
    Hi!

    If you use PDL (Perl Data Language http://pdl.perl.org/), you can collapse dimensions of piddles using the function "clump". This will allow you to do what you want in amazingly few steps:
    $a = pdl @your_array; $b = clump($a,2); # collapses the first two dimensions print $b;


    Hope this helps!

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