Following the educational tradition of:

• Rosetta code
• 99 Lisp Problems
• Five Ways to Reverse a String of Words (C#, Perl 5, Perl 6, Ruby, Haskell)
• Yet Another Rosetta Code Problem (Perl, Ruby, Python, Haskell, ...)

this meditation describes an arbitrary problem to be solved in different ways and in different languages.

The Problem

Given a list of strings, for example ("a", "bb", "c", "d", "e", "f", "g", "h"), and a chunksize, for example 3, write a subroutine to return a multi-line string, for example:

a bb c
d e f
g h
[download]

The output string must contain a single space between each array element and a newline every chunksize items. Note that no trailing space is permitted on any line and the last line must be properly newline-terminated.

Perl

Here was my first Perl attempt:

use strict;
use warnings;

sub chunk_array {
    my ($n, @vals) = @_;
    my $str;
    my $i = 0;
    for my $v (@vals) {
        ++$i;
        $str .= $v . ( ($i % $n) ? " " : "\n" );
    }
    substr($str, -1, 1) = "\n";
    return $str;
}

my $v1 = chunk_array(3, "a", "bb", "c", "d", "e", "f", "g", "h");
$v1 eq "a bb c\nd e f\ng h\n" or die "error: '$v1'\n";
print $v1;

my $v2 = chunk_array(3, "a", "bb", "c", "d", "e", "f");
$v2 eq "a bb c\nd e f\n" or die "error: '$v2'\n";
print $v2;
[download]

I trust this initial solution will clarify the problem specification.

Being dissatisfied with this ugly first attempt, I next took at a look at the core List::Util and the non-core List::MoreUtils modules, writing two different solutions using List::MoreUtils, one using natatime, the other part, as shown below:

use List::MoreUtils qw(part natatime);

sub chunk_array {
    my ($n, @vals) = @_;
    my $str;
    my $iter = natatime($n, @vals);
    while ( my @line = $iter->() ) {
        $str .= join(" ", @line) . "\n";
    }
    return $str;
}

sub chunk_array {
    my ($n, @vals) = @_;
    my $i = 0;
    return join "", map { join(" ", @$_)."\n" } part { $i++/$n } @vals
+;
}
[download]

Python

For cheap thrills, I hacked out a Python itertools-based solution.

from itertools import *

def group(n, iterable):
  args = [iter(iterable)] * n
  return izip_longest(*args)

def chunk_array(n, vals):
  return "".join(" ".join(x for x in i if x!=None)+"\n" for i in group
+(n, vals))
[download]

Discussion

I've derived little enjoyment so far from any of my solutions and accordingly encourage you to show us a more elegant way to solve this simple problem.

Please feel free to contribute more Perl solutions or a solution in any language you fancy. I'm especially eager to admire a Perl 6 solution.

Update: See also Re: How to Split on specific occurrence of a comma (2020)

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