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
How this can be done in Ruby?
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Later, similar question, not worded in terms of Python, with more answers: stackoverflow.com/questions/3343861/…Dave Schweisguth– Dave Schweisguth2017-07-29 02:37:52 +00:00Commented Jul 29, 2017 at 2:37
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2 Answers
Use the include?() method:
(1..10).include?(5) #=>true
(1..10).include?(16) #=>false
EDIT:
(1..10) is Range in Ruby , in the case you want an Array(list) :
(1..10).to_a #=> [1,2,3,4,5,6,7,8,9,10]
2 Comments
noomz
So this is like index() methods that return nil(false) or index(true)?
pierrotlefou
Index works only on Array but not on Range. !(1..10).to_a.index(5).nil? equals (1..10).include?(5). Obviously, latter is better.
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
3 Comments
mthurlin
This only applies to ranges, the OP asked for lists (and used range only as an example of a list)
johannes
he wrote list list but used a Range in his example, so I think he want's a range. It seems as there is no native way in Python to create a range which is not a list. (but I must point out, I am no python expert, so my assumption may be wrong)
noomz
In python, there's no range type. So range(10) is to generated [0,1,2,3,4,5,6,7,8,9] list that's (0..9) in ruby (for precisely, it's xrange(10) that's generator which yield value only when you want it). For this case, I didn't notice which type is it before because I used "gets.split.each". Btw, this's a very nice answer!