Thanks for this comment, I never heard about this third argument. Here is the updated script:

use strict;
use warnings;
use Data::Dumper;

my $command = "ps -f";
my $id = "PID";

my @ps =`$command`;
$ps[0] =~ s/^\s*//;
my @header = split /\s+/, shift @ps;
my ($posid) = grep { $header[$_] eq $id } 0..$#header;
die "$id: No such column!\n" unless defined( $posid );
splice @header, $posid, 1;

my %psdata;
while( @ps ) {
  my $row = shift @ps;
    chomp $row;
  $row =~ s/^\s*//;
  my @row = split /\s+/, $row, $#header+2;
  my $this_id = splice @row, $posid, 1;
  @{$psdata{$this_id}}{@header} = @row;
}

print Dumper( %psdata );
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