d_zero - 1 year ago 59
Ruby Question

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

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
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.

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
``````
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