# ETOOBUSY ðŸš€ minimal blogging for the impatient

# PWC186 - Zip List

**TL;DR**

Here we are with TASK #1 from The Weekly Challenge #186. Enjoy!

# The challenge

You are given two list

`@a`

and`@b`

of same size.Create a subroutine

`sub zip(@a, @b)`

that merge the two list as shown in the example below.

Example`Input: @a = qw/1 2 3/; @b = qw/a b c/; Output: zip(@a, @b) should return qw/1 a 2 b 3 c/; zip(@b, @a) should return qw/a 1 b 2 c 3/;`

# The questions

Uhmâ€¦ I guess I can nitpick a bit and observe that `@a`

and `@b`

are
two *arrays*. For everything else, Iâ€™ll trust that the user of the
function feeds in the input stuff exactly as stated.

# The solution

The nitpicking in the questions section is not merely to nag our fine host.

If we indeed have two *arrays*, then we can implement functions that
expect arrays. So in Raku we would have:

```
#!/usr/bin/env raku
use v6;
sub MAIN {
my @a = <1 2 3>;
my @b = <a b c>;
zip(@a, @b).say;
zip(@b, @a).say;
}
sub zip (@a, @b) { (@a Z @b).flat }
```

Donâ€™t askâ€¦ but yes, I missed the

`.flat`

in the first try.

In Perl we can do some prototypes magic (`perldoc perlsub`

if youâ€™re
curious) and obtain a similar result:

```
#!/usr/bin/env perl
use v5.24;
use warnings;
sub zip(\@\@);
my @a = qw< 1 2 3 >;
my @b = qw< a b c >;
say "(@{[ zip(@a, @b) ]})";
say "(@{[ zip(@b, @a) ]})";
sub zip (\@\@) {
my ($A, $B) = @_;
map { ($A->[$_], $B->[$_]) } 0 .. $A->$#*;
}
```

On the other hand, if weâ€™re dealing with the looser concept of *lists*,
and for example we first merge the two arrays into a single one and then
feed it as a list of items, bad things will happen. In Perl terms:

```
say "(@{[ zip(@{[ @a, @b ]}) ]})";
# Not enough arguments for main::zip...
```

So, of course, we can look at the problem from a pure list angle, and assume that we will be given a single list composed of an even number of elements, which we can split into two parts that we can then zip:

```
sub listy_zip {
my @A = splice @_, 0, @_ / 2;
my @B = @_
map { ($A[$_], $B[$_]) } 0 .. $#A;
}
```

We might even cheat a bit with this implementation and (ab)use signatures:

```
sub listy_zip (@B, @A) {
@A = splice @B, 0, @B / 2;
map { ($A[$_], $B[$_]) } 0 .. $#A;
}
```

This would be blatant lying, right?

Stay safe!

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