Ruby: How do I join elements of an array together with a prefix?

Question

I have an array like so:

["marblecake", "also", "the", 1337]

I would like to get back a string which contains each element of the array prefixed by some specified string, then joined together by another specified string. For example,

["marblecake", "also", "the", 1337].join_with_prefix("%", "__")

should result in

# => %marblecake__%also__%the__%1337

How might I do this?

Answer 1

If your array is in "a" then this one-liner will do it

a.map! { |k| "%#{k}" }.join("_")

You could easily put this in a function of your own - even add it to the Array class so that you can call it on an array, like in your example.

Answer 2

As per the above suggestion:

class Array
  def join_with_prefix(prefix,separator)
    self.collect {|e| prefix.to_s + e }.join(separator)
  end
end

p ['ab','cd','ef'].join_with_prefix('%','__')

=> "%ab__%cd__%ef"

Answer 3

All previous answers are extremely stupid. The simplest and the fastest method is this:

class Array
  def join_with_prefix(prefix, separator)
    prefix + self.join(separator + prefix)
  end
end