```On Mar 28, 2006, at 2:08 AM, Eric Luo wrote:

> I want to make a Array multipled by another Array, and the
> following semantic.
> For example:
>  [1, 2, 3] * [4, 5]
> then I will want [[1, 4], [1, 5], [2, 4], [2, 5], [3, 4], [3, 5]]
> returned.

a = [1, 2, 3]
b = [4, 5]

(a * b.size).zip(b * a.size).sort
# => [[1, 4], [1, 5], [2, 4], [2, 5], [3, 4], [3, 5]]

# or w/o sort:
a.zip(a).flatten.zip(b * a.size)
# => [[1, 4], [1, 5], [2, 4], [2, 5], [3, 4], [3, 5]]

# the latter only works as-is because b.size == 2 (a.zip(a).flatten
~= a * 2).
# If b.size were 3, you'd add b.size-1 a's to the first zip arg list:

b << 6
a.zip(a, a).flatten.zip(b * a.size)
# => [[1, 4], [1, 5], [1, 6], [2, 4], [2, 5], [2, 6], [3, 4], [3, 5],
[3, 6]]

# if order doesn't actually matter, the first solution is the cleanest:

class Array
def x(b)
a = self
(a * b.size).zip(b * a.size)
end
end

a.x b
=> [[1, 4], [2, 5], [3, 6], [1, 4], [2, 5], [3, 6], [1, 4], [2, 5],
[3, 6]]

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```