In Ruby, how do I find out if a string is not in an array?

do this if not ["www", "blog", "foo", "bar"].include?(current_subdomain)

or you can use grep

>> d=["www", "blog", "foo", "bar"]
>> d.grep(/^foo$/)
=> ["foo"]
>> d.grep(/abc/)
=> []

Besides using an array, you can also do this:

case current_subdomain
when 'www', 'blog', 'foo', 'bar'; do that
else do this
end

This is actually much faster:

require 'benchmark'
n = 1000000

def answer1 current_subdomain
  case current_subdomain
  when 'www', 'blog', 'foo', 'bar'
  else nil
  end
end

def answer2 current_subdomain
  nil unless  ["www", "blog", "foo", "bar"].include?(current_subdomain)
end

Benchmark.bmbm do |b|
  b.report('answer1'){n.times{answer1('bar')}}
  b.report('answer2'){n.times{answer2('bar')}}
end

Rehearsal -------------------------------------------
answer1   0.290000   0.000000   0.290000 (  0.286367)
answer2   1.170000   0.000000   1.170000 (  1.175492)
---------------------------------- total: 1.460000sec

              user     system      total        real
answer1   0.290000   0.000000   0.290000 (  0.282610)
answer2   1.180000   0.000000   1.180000 (  1.186130)


Benchmark.bmbm do |b|
  b.report('answer1'){n.times{answer1('hello')}}
  b.report('answer2'){n.times{answer2('hello')}}
end

Rehearsal -------------------------------------------
answer1   0.250000   0.000000   0.250000 (  0.252618)
answer2   1.100000   0.000000   1.100000 (  1.091571)
---------------------------------- total: 1.350000sec

              user     system      total        real
answer1   0.250000   0.000000   0.250000 (  0.251833)
answer2   1.090000   0.000000   1.090000 (  1.090418)

You can try exclude? method instead of include?

Example:

do_this if ["www", "blog", "foo", "bar"].exclude?(current_subdomain)

Hope this help...Thanks

Edited: This function is applicable only for Rails (ActiveSupport), not native Ruby.

do_this unless  ["www", "blog", "foo", "bar"].include?(current_subdomain)

or

do_this if not ["www", "blog", "foo", "bar"].include?(current_subdomain)

I'm using the Array#include? method.

However using unless is a fairly big ruby idiom.