khpeek - 1 year ago 41

Ruby Question

As part of an exercise, I'm trying to implement the bubble sort algorithm in two different ways.

For the first part, I've implemented the bubble sort algorithm as an Array instance method as follows:

`class Array`

def bubble_sort!

sorted=false

until sorted

sorted=true

for i in (0...self.length-1)

if self[i]>self[i+1]

self[i],self[i+1]=self[i+1],self[i]

sorted=false

end

end

end

self

end

end

so that, for example,

`[5,2,4].bubble_sort!`

returns [2,4,5]. The next part of the exercise is to modify the method so that it takes a block to perform the comparison:

`[1, 3, 5].bubble_sort! { |num1, num2| num1 <=> num2 } #sort ascending`

[1, 3, 5].bubble_sort! { |num1, num2| num2 <=> num1 } #sort descending

In order to not repeat myself, I've tried to implement this as follows:

`class Array`

def bubble_sort!(&prc)

if block_given?

boolean_operator = Proc.new {|a,b| prc.call(a,b)==1}

else

boolean_operator = Proc.new {|a,b| a>b}

end

sorted=false

until sorted

sorted=true

for i in (0...self.length-1)

# if self[i]>self[i+1]

if boolean_operator(self[i],self[i+1])

self[i],self[i+1]=self[i+1],self[i]

sorted=false

end

end

end

self

end

However, if I try to test this with

`p [5,2,4].bubble_sort! {|x,y| x<=>y}`

I get the following error:

`in `bubble_sort!': undefined method `boolean_operator' for [5, 2, 4]:Array (NoMethodError)`

It seems like the "boolean_operator" is somehow not defined where it is invoked (also not if I remove the block in the input). I understand that Ruby doesn't have nested methods, but I thought that defining procs and lambdas within a method was possible?

Answer

The issue here is you're treating the variable you've defined as a Proc like it's a method (on the Array class, hence the NoMethodError). The proper way to call the proc is as follows:

`boolean_operator.call(self[i],self[i+1])`

Source (Stackoverflow)