Read coordinates

[Berk Birand]

Hi,

I am new to Perl (as a matter of fact, I started learning it a couple of
days ago; I have some previous programming experience though). When
looking for the ideal languages to use for a particular project, I came
across perl, and starting writing the script.

I need to read a text containing some coordinates:
248,156
322,156
326,368
248,368

326,194
950,194
960,360
326,364

....

I need to process these coordinates and find the center of gravity of the
structure.

For now I have this code.

#! /usr/bin/env perl

open(HELL,"plc" ) or die "Can't open plc: $!";
my @x;
my @y;

#first read the file
#put the coordinates in special variables

while (<HELL>) { # assigns each line in turn to $_
$_ =~ /(\d+),(\d+)/;

for($i=0; $i<=3;$i++) {
@x[$i] = [ $1 ] ;
@y[$i] = [ $2 ];

print $x[1]; }

# print "the x is $1 \n";
# print "the y is $2 \n";
# print "Just read in this line: $_";

# do the necessary calculations
# [...]
}
I thought about putting each coordinate in an array of x and y values, and
then finding their arithmetic means.
However I do not know how to augment the arrays size at each iteration of
while. The size of the array cannot be changed can it?
Help would be greatly appreciated!

Thanks

BB

[Jürgen Exner]

Re: Read coordinates

Berk Birand wrote:
[...][color=blue]
> However I do not know how to augment the arrays size at each
> iteration of while. The size of the array cannot be changed can it?[/color]

I think you are looking for the push() function, see "perldoc -f push"

jue

[Berk Birand]

Re: Read coordinates

On Sun, 07 Mar 2004 00:25:49 +0000, Jürgen Exner wrote:[color=blue]
> I think you are looking for the push() function, see "perldoc -f push"[/color]

Yes, that solved the problem quite well.
Thanks Jürgen.

[Jim Gibson]

Re: Read coordinates

In article <41ed1ab461951f 4a2a1d604f4a0ea 5d5@news.terane ws.com>, Berk
Birand <graffitiNOSPAM @NOSPAMyahoo.co m> wrote:
[color=blue]
> Hi,
>
> I am new to Perl (as a matter of fact, I started learning it a couple of
> days ago; I have some previous programming experience though). When
> looking for the ideal languages to use for a particular project, I came
> across perl, and starting writing the script.
>
> I need to read a text containing some coordinates:
> 248,156
> 322,156
> 326,368
> 248,368
>
> 326,194
> 950,194
> 960,360
> 326,364
>
> ...
>
> I need to process these coordinates and find the center of gravity of the
> structure.
>
> For now I have this code.
>
> #! /usr/bin/env perl
>[/color]

You should let Perl help you while you are developing code:

use strict;
use warnings;
[color=blue]
> open(HELL,"plc" ) or die "Can't open plc: $!";
> my @x;
> my @y;
>
> #first read the file
> #put the coordinates in special variables
>[/color]

my $i = 0; #(see below)
[color=blue]
> while (<HELL>) { # assigns each line in turn to $_
> $_ =~ /(\d+),(\d+)/;[/color]

Always check to see if the match worked before using the results:

if( /(\d+), (\d+)/ ) {[color=blue]
>
> for($i=0; $i<=3;$i++) {[/color]

Why are you assigning the extracted coordinates 4 times?
[color=blue]
> @x[$i] = [ $1 ] ;[/color]

This is assigning a reference to an array of one element ( [ $1 ] ) to
an array slice of one element ( @x[$i] ). This is not likely to be what
you want.[color=blue]
> @y[$i] = [ $2 ];[/color]

Maybe you want just:

$x[$i] = $1;
$y[$i] = $2;
$i++;

where you refer to the n'th element of @x as $x[n]. If so, then you
need the declaration of $i above, before and outside the loop.
[color=blue]
>
> print $x[1]; }
>
> # print "the x is $1 \n";
> # print "the y is $2 \n";
> # print "Just read in this line: $_";
>
> # do the necessary calculations
> # [...]
> }[/color]

Now you can do a calculation with the contents of @x and @y:

for my $i ( 0 .. $#x ) {
print "$x[$i], $y[$i]\n";
}
[color=blue]
> I thought about putting each coordinate in an array of x and y values, and
> then finding their arithmetic means.
> However I do not know how to augment the arrays size at each iteration of
> while. The size of the array cannot be changed can it?
> Help would be greatly appreciated!
>
> Thanks
>
> BB
>
>[/color]