Ruby methods equivalent of “if a in list” in python?

Question

In python I can use this to check if the element in list a:

>>> a = range(10)
>>> 5 in a
True
>>> 16 in a
False
         


        

Answer 1

Range has the === method, which checks whether the argument is part of the range.

You use it like this:

(1..10) === 5  #=> true
(1..10) === 15 #=> false

or as you wrote it:

a= (1..10)
a === 5  #=> true
a === 16 #=> false

You must be sure the values of the range and the value you are testing are of compatible type, otherwise an Exception will be thrown.

(2.718..3.141) === 3 #=> true
(23..42) === "foo"   # raises exception

• This is done in O(1), as Range#===(value) only compares value with Range#first and Range#last.
• If you first call Range#to_a and then Array#include?, it runs in O(n), as Range#to_a, needs to fill an array with n elements, and Array#include? needs to search through the n elements again.

If you want to see the difference, open irb and type:

(1..10**9) === 5            #=> true
(1..10**9).to_a.include?(5) # wait some time until your computer is out of ram and freezess