How can I pass in a block to my "bubble sort" method? - ruby

Question

The below code is my newbie take on a bubble sort method.
#For each element in the list, look at that element and the element
#directly to it's right. Swap these two elements so they are in
#ascending order.
def bubble_sort (array)
a = 0
b = 1
until (array.each_cons(2).all? { |a, b| (a <=> b) <= 0}) == true do
sort = lambda {array[a] <=> array[b]}
sort_call = sort.call
loop do
case sort_call
when -1 #don't swap
a += 1
b += 1
break
when 0 #don't swap
a += 1
b += 1
break
when 1 #swap
array.insert(a,array.delete_at(b))
a += 1
b += 1
break
else #end of array, return to start
a = 0
b = 1
break
end
end
end
puts array.inspect
end
array = [4, 2, 5, 6, 3, 23, 5546, 234, 234, 6]
bubble_sort(array)
I want to be able to alter this method so that it takes a block of code as an argument and uses this to determine how it sorts.
For example:
array = ["hello", "my", "name", "is", "daniel"]
bubble_sort(array) {array[#a].length <=> array[#b].length}
(When I've tried this I've turned a and b into instance variables throughout the code.)
I have tried using yield but I get undefined method 'length' for nil:NilClass once the end of the array is reached. I've tried adding in things such as
if array[#b+1] == nil
#a = 0
#b = 1
end
This helps but I still end up with weird problems like infinite loops or not being able to sort more than certain amount of elements.
Long story short, I have been at this for hours. Is there a simple way to do what I want to do? Thanks.

Answer 1

The way you're calling your lambda is a bit odd. It's actually completely unnecessary. I refactored your code and cleaned up a bit of the redundancy. The following works for me:
def sorted?(arr)
arr.each_cons(2).all? { |a, b| (a <=> b) <= 0 }
end
def bubble_sort (arr)
a = 0
b = 1
until sorted?(arr) do
# The yield call here passes `arr[a]` and `arr[b]` to the block.
comparison = if block_given?
yield(arr[a], arr[b])
else
arr[a] <=> arr[b]
end
if [-1, 0, 1].include? comparison
arr.insert(a, arr.delete_at(b)) if comparison == 1
a += 1
b += 1
else
a = 0
b = 1
end
end
arr
end
sample_array = [4, 2, 5, 6, 3, 23, 5546, 234, 234, 6]
# Sanity check:
100.times do
# `a` is the value of `arr[a]` in our function above. Likewise for `b` and `arr[b]`.
print bubble_sort(sample_array.shuffle) { |a, b| a <=> b }, "\n"
end
EDIT
A cleaner version:
# In place swap will be more efficient as it doesn't need to modify the size of the arra
def swap(arr, idx)
raise IndexError.new("Index #{idx} is out of bounds") if idx >= arr.length || idx < 0
temp = arr[idx]
arr[idx] = arr[idx + 1]
arr[idx + 1] = temp
end
def bubble_sort(arr)
loop do
sorted_elements = 0
arr.each_cons(2).each_with_index do |pair, idx|
comparison = if block_given?
yield pair.first, pair.last
else
pair.first <=> pair.last
end
if comparison > 0
swap(arr, idx)
else
sorted_elements += 1
end
end
return arr if sorted_elements >= arr.length - 1
end
end
# A simple test
sample_array = [4, 2, 2, 2, 2, 2, 5, 5, 6, 3, 23, 5546, 234, 234, 6]
sample_str_array = ["a", "ccc", "ccccc"]
100.times do
print bubble_sort(sample_array.shuffle) { |a, b| a <=> b }, "\n"
print bubble_sort(sample_str_array.shuffle) { |a, b| a.length <=> b.length }, "\n"
end

Answer 2

You're not too far off. Just a few things:
Make your function take a block argument
def bubble_sort (array, &block)
Check to see if the user has provided a block
if block_given?
# Call user's comparator block
else
# Use the default behavior
end
Call the user's comparator block
block.call(a, b)
In the user-provided block, accept block params for the elements to compare
bubble_sort(array) {|a,b| a.length <=> b.length}
That should put you in the right ballpark.