Ruby comes with overloaded operator &, using which intersection of two array is childish.
For example:
#!/usr/bin/env ruby
a=[1, 2, 3, 4]
b=[1, 2, 2 ,3 ,4, 5, 6]
c= a & b #intersection of 'a' and 'b' arrays
print c
will produce: 1 2 3 4
And for example this:
#!/usr/bin/env ruby
a=['aa', 'ac', 'acb', 'acbd']
b=[ 'ac', 'acb', 'bca', 'zwx']
c= a & b #intersection of 'a' and 'b' arrays
puts c
will produce: ac acb
Everything is OK, when you perform intersection of standard types, like String or Integers, etc.
However, there is problem when you create your own class, and try to perform intersection of array of objects of your class.
#!/usr/bin/env ruby
class MyClass #my own very simple class
attr_reader :var1, :var2
def initialize(arg1,arg2)
@var1 = arg1
@var2 = arg2
end
def to_s
"#{var1}: #{var2}"
end
end
a = [MyClass.new('house',3), MyClass.new('mouse',5)]
b = [MyClass.new('cat',3), MyClass.new('house',5), MyClass.new('mouse',5)]
c = a & b #INTERSECTION !!!
puts c
This, unfortunately gives nothing!
After a while I found solution to that. The solution is: you must overload eql? and hash functions in you class. Java programmers should now something, because as I remember in Java, you do something similar while working especially with Comparable interface.
So, to make intersection, final example my program looks like this:
#!/usr/bin/env ruby
class MyClass attr_reader :var1, :var2
def initialize(arg1,arg2)
@var1 = arg1
@var2 = arg2
end
def to_s
"#{var1}: #{var2}"
end
def eql? other #OVERLOADED eql? !!!
other.kind_of?(self.class) && @var1 == other.var1
end
def hash #OVERLOADED hash !!!
@var1.hash #use var1 hash value,
#as hash for MyClass
end
end
a = [MyClass.new('house',3), MyClass.new('mouse',5)]
b = [MyClass.new('cat',3), MyClass.new('house',5), MyClass.new('mouse',5)]
c = a & b #INTERSECTION !!!
puts c
house: 3
mouse: 5
I used only standard hash value from @var1 in my class, because I was only interested in making intersection based on @var1, nevertheless there is noting against to make more complex hash and eql? function.
