Help separating arrays?

I'm working on a project that receives an array of data that looks like
this (example):

@fieldspecs = qw
(
JobNum 14
ProjectID 25
PartNum2 50
ProdQty13 15.2
);

The array is a definition of fields in a file; the fieldname followed by
the field width. The fieldname frequently contains digits. When I get
the data, it is text so I put it in an array (like you see above)
because it is important to reference the fieldnames in the order I
receive them. The array ALWAYS has a fieldname followed by the width,
the the number of elements is always divisible by two.

However, I also want to access the data as a hash so that for a given
fieldname I can easily grab the width.

It is easy enough to convert this array to a hash, but...

....is there a Perl-ish way to either ram the *fieldnames only* into a
new array, OR, delete the field widths from the array leaving only the
fieldnames??

Barry Brevik
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Re: Help separating arrays?

On Jan 22, 2008, at 5:15 p, Barry Brevik wrote:

> I'm working on a project that receives an array of data that looks
> like
> this (example):
>
> @fieldspecs = qw
> (
> JobNum 14
> ProjectID 25
> PartNum2 50
> ProdQty13 15.2
> );
>
> The array is a definition of fields in a file; the fieldname
> followed by
> the field width. The fieldname frequently contains digits. When I get
> the data, it is text so I put it in an array (like you see above)
> because it is important to reference the fieldnames in the order I
> receive them. The array ALWAYS has a fieldname followed by the width,
> the the number of elements is always divisible by two.
>
> However, I also want to access the data as a hash so that for a given
> fieldname I can easily grab the width.
>
> It is easy enough to convert this array to a hash, but...
>
> ...is there a Perl-ish way to either ram the *fieldnames only* into a
> new array, OR, delete the field widths from the array leaving only the
> fieldnames??
>
>

assuming you want the field names to end up in @names:

my @names = grep { ! m/^\d+$/ } @fieldspecs; # works if your
fieldnames are never *all* numeric

or

my %names = (@fieldspecs);
my @names = keys %names; # works if the files are *always* evenly paired

--Chris
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Re: Help separating arrays?

Barry Brevik wrote:
> I'm working on a project that receives an array of data that looks like
> this (example):
>
> @fieldspecs = qw
> (
> JobNum 14
> ProjectID 25
> PartNum2 50
> ProdQty13 15.2
> );
>
> The array is a definition of fields in a file; the fieldname followed by
> the field width. The fieldname frequently contains digits. When I get
> the data, it is text so I put it in an array (like you see above)
> because it is important to reference the fieldnames in the order I
> receive them. The array ALWAYS has a fieldname followed by the width,
> the the number of elements is always divisible by two.
>
> However, I also want to access the data as a hash so that for a given
> fieldname I can easily grab the width.
>
> It is easy enough to convert this array to a hash, but...
>
> ...is there a Perl-ish way to either ram the *fieldnames only* into a
> new array, OR, delete the field widths from the array leaving only the
> fieldnames??

One way you could do it is by using a counter variable inside of a grep
block, like so:

my $n;
my @fieldnames = grep { $n++ % 2 == 0 } @fieldspecs;


You mentioned that your project "receives" the data, so I wonder if
there's a point in your program where you're stuffing it into the
@fieldspecs array.

If there is, you could maintain two arrays:

my $input = "JobNum 14\n ProjectID 25 \n PartNum2 50\n";

my @names;
my @widths;
foreach (split /\n/, $input) {
my ($name, $width) = /(\w+)\s+([\d\.]+)/;

push @names, $name;
push @widths, $width;
}

Then, the indexes for the names and widths will match up, and you can do
things like

for my $i (0..$#names) {
my $name = $names[$i];
my $width = $widths[$i];

# do whatever here
}


Chris Prather wrote:
> my %names = (@fieldspecs);
> my @names = keys %names; # works if the files are *always* evenly paired

The problem with this is that it doesn't preserve order.

$ perl -le 'my %names = qw(a 1 b 1 c 1); print join(", ", keys %names);'
c, a, b


Hope that gives you some options!

--
Mike Gillis
ActiveState Software
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RE: Help separating arrays?

On Tue, 22 Jan 2008, Chris Prather wrote:
> my %names = (@fieldspecs);
> my @names = keys %names; # works if the files are *always* evenly paired

There is no need for the temporary variable (unless you can make some
other use of the hash anyways); you can just create an anonymous hash
reference:

my @names = keys %{{@fieldspecs}};

But, as Mike already mentioned, this will not preserve the original
order of the field names.

Cheers,
-Jan

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RE: Help separating arrays?

Mike Gillis <> wrote:
> Chris Prather wrote:
>> my %names =3D (@fieldspecs);
>> my @names =3D keys %names; # works if the files are *always* evenly
>> paired
> =

> The problem with this is that it doesn't preserve order.
> =

> $ perl -le 'my %names =3D qw(a 1 b 1 c 1); print join(", ", keys
> %names);' =

> c, a, b

You can preserve the order with Tie::IxHash, e.g.

--------------------------------------
use strict;
use warnings;

use Tie::IxHash;

my @fieldspecs =3D qw
(
JobNum 14
ProjectID 25
PartNum2 50
ProdQty13 15.2
);

tie my %hash, "Tie::IxHash", @fieldspecs;
my @names =3D keys %hash;
print "@names\n";
--------------------------------------

.... or alternatively, if you don't want to use a hash, just extract the
array entries with even indices:

my @names =3D @fieldspecs[grep {$_ % 2 == 0} 0..$#fieldspecs];
print "@names\n";

HTH

-- =

Brian Raven =


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