@set = (
                [ 'file00.csv', 'file01.csv', 'file02.csv', ],
                [ 'file03.csv', 'file04.csv', 'file05'csv', ],
                [ 'file06.csv', 'file07.csv', ],
                [ 'file08.csv', 'file09.csv', ],
                [ 'file10.csv', 'file11.csv', ],
            )
##</code><code>##

    # my $n              = 5;
    my @set;
    my $file_count;
    my $partition_size;
    my $remainder;

    $file_count     = scalar @file;                   # 12
    if ( $file_count >= $n ) {
        $partition_size = int( $file_count / $n );    # 2
        $remainder      = $file_count % $n;           # 2
    }
    else {
        $partition_size = 1;
        $remainder = 0;
    }
    my $i = 0;
    while ( scalar @file ) {
        foreach my $j ( 1 .. $partition_size ) {
            my $fn = shift @file;
            push @{$set[$i]}, $fn;
        }
        if ( $i < $remainder ) {
            my $fn = shift @file;
            push @{$set[$i]}, $fn;
        }
        $i++;
    }

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

use Cwd;
use Data::Dumper;
use Getopt::Long;
use IO::Compress::Gzip qw( $GzipError );
use Text::CSV;

$Data::Dumper::Deepcopy = 1;
$Data::Dumper::Sortkeys = 1;

$| = 1;
srand();

my $output_files = 5;
my $outfile_name = $0 . q{.csv};
my $path         = q{./};

$outfile_name =~ s/\.pl.*$//g;

GetOptions(
    q{help} => sub {
        &help(
            output_files => $output_files,
            outfile_name => $outfile_name,
            path         => $path,
        );
    },
    q{output_files:i} => \$output_files,
    q{outfile_name:s} => \$outfile_name,
    q{path:s}         => \$path,
);

my $start_dir = getcwd;

if ( !-d $path ) {
    die qq{Directory $path not found: $!\n};
}

my @file = get_files( path => $path, );
my @set =
  partition_files( files => \@file, n => $output_files, );
write_subfiles( set => \@set, prefix => $outfile_name, );

#
# Subroutines
#
sub help {
    my ( %param, ) = @_;

    print sprintf
      <<HELP_TEXT, $param{outfile_name}, $param{output_files}, $param{path};

Usage:
        $0
        $0 [--help]
        $0 [--max_lines N] [--outfile_name str] [--path str]

Where:
    outfile_name str       - Output filename prefix
                               (naming will be {prefix}-nn.csv;
                               default: %s).
    output_files N         - Device data into at most N files
                               (data in the same input file
                               will appear in the same file;
                               default: %d).
    path str               - Path to process
                               (default: %s).

HELP_TEXT
    exit;
}

sub get_files {
    my ( %param, ) = @_;

    my @file = ();

    if ( !exists $param{path} ) {
        return @file;
    }

    opendir my $dir, $param{path} or die $!;
    while ( my $fn = readdir($dir) ) {
        next if ( $fn =~ m/^.{1,2}$/ );
        next unless ( $fn =~ m/\.csv$/i );
        push @file, $fn;
    }
    closedir $dir;

    @file = sort { -s $a <=> -s $b } @file;

    return @file;
}

sub partition_files {
    my (%param) = @_;

    my @set;

    my $file_count;
    my $partition_size;
    my $remainder;

    my $n    = $param{n};
    my @file = @{ $param{files} };

    $file_count = scalar @file;    # 12
    if ( $file_count >= $n ) {
        $partition_size = int( $file_count / $n );    # 2
        $remainder      = $file_count % $n;           # 2
    }
    else {
        $partition_size = 1;
        $remainder      = 0;
    }
    my $i = 0;
    while ( scalar @file ) {

        foreach my $j ( 1 .. $partition_size ) {
            my $fn = shift @file;
            push @{ $set[$i] }, $fn;
        }
        if ( $i < $remainder ) {
            my $fn = shift @file;
            push @{ $set[$i] }, $fn;
        }
        $i++;
    }

    return @set;
}

sub write_subfiles {
    my (%param) = @_;

    my @set    = @{ $param{set} };
    my $prefix = $param{prefix};

    my $name_format =
        $prefix . q{-} . q{%0}
      . int( log( scalar @set ) / log(10) + 1 + 1 ) . q{d}
      . q{.csv} . q{.gz};

    my $csv =
      Text::CSV->new(
        { binary => 1, auto_diag => 1, eol => $/, } );

    foreach my $i ( 0 .. $#set ) {
        my $fn = sprintf $name_format, $i;

        my $z = new IO::Compress::Gzip $fn,
          -Level => IO::Compress::Gzip::Z_BEST_COMPRESSION,
          or die
          qq{IO::Compress::Gzip failed: $GzipError\n};

        foreach my $ifn ( @{ $set[$i] } ) {
            my $flag = 1;
            open my $ifh, q{<:encoding(utf8)}, $ifn
              or die qq{$ifn: $!};
            while ( my $row = $csv->getline($ifh) ) {
                if ($flag) {
                    $flag--;
                    next;
                }
                my $status = $csv->print( $z, $row, );
                $row = undef;
            }
            close $ifh;
        }
        $z->close;
    }
}