Perl: printing array's index and value

craig467 · 08-30-2006, 09:48 AM

Is there a way to print a out an array's index AND value using a foreach loop?

I have an array similar to this
my @numbers = (2,5,4,2,6,3,7);

I want to have printout on screen like this:
0 2
1 5
2 4
3 2
4 6
5 3
6 7

I can get the values to print out themselves, but I can not get the indexes to print.

Thanks.

xhi · 08-30-2006, 10:12 AM

well the most obvious solution would be to have a loop counter. start it at 0 and print and increment every time through the loop

craig467 · 08-30-2006, 10:24 AM

I could do that but I was wondering if there was a way to obtain the index since it is already "available". Is there away to grab it from the array?

homey · 08-30-2006, 10:30 AM

Using the built in $. but, it starts at 1 not 0 .

Code:

perl -ne 'print "$.. $_"' file.txt

craig467 · 08-30-2006, 10:57 AM

Bummer, I was realy hoping there would be a way to capture the index number like the way you can with a hash (keys function).

xhi · 08-30-2006, 11:53 AM

Quote:

Originally Posted by homey

Using the built in $. but, it starts at 1 not 0 .

Code:

perl -ne 'print "$.. $_"' file.txt

but that only works for lines read from an opened file handle, it has nothing to do with an index of an array.

makyo · 08-30-2006, 01:26 PM

Hi.

Similar to keys:

Code:

#!/usr/bin/perl

# @(#) p1       Demonstrate index with array.

use warnings;
my @numbers = (2,5,4,2,6,3,7);

foreach my $i ( 0..$#numbers ) {
        print "$i $numbers[$i]\n";
}

Resulting in:

Code:

craig467 · 08-30-2006, 03:29 PM

Makyo,

I am just a beginner at Perl and I have not seen this syntax (0..$#numbers) before so I will have to read up on that, but it works great and I really appreciate it!

Thanks!!!

makyo · 08-30-2006, 03:50 PM

Hi, craig467.

You're welcome.

As you will see, the ".." operator means range from least to greatest, so in the script an array of those values is generated -- you need to be careful of that, so that you don't declare an array of a few million -- although that may be a good experiment so that you can see the result.

Because perl handles so many details for you, it knows all about the basic data structures, including specific array lengths. The "$#name" construct is a way that perl provides the value of the index of the last element -- essentially the length-1.

If you are going to do serious programing in perl, I recommend Perl Best Practices, D Conway. Just keep on writing code -- one way is to check forums daily for questions and answers, and try to solve problems that look interesting.

Best wishes ... cheers, makyo