Sorting strings in array without sorting function - Ruby - ruby

Question

I'm trying to create a sorting algorithm without the sorting function in Ruby. I've based it of the idea of insertion sort. The idea is that the function checks whether the nth value of each two words are same, and if so n increases by one until one value is larger than the other. In that case the words might get switched. However, my function keeps freezing. Any ideas why?
words = ["my","favorite","animal", "are", "the", "elephant", "and", "the", "antelope", "and", "the", "favela"]
#Convert all letters into numbers. Output individual words as arrays.
converted_words = words.map(&:chars).map { |letters| letters.map { |letter| letter.to_i 36 } }
puts converted_words.to_s
i = 1
x = 0
while i < converted_words.length
if converted_words[i][x] == converted_words[i-1][x]
x = x + 1
else
if converted_words[i][x] < converted_words[i-1][x]
converted_words[i], converted_words[i-1] = converted_words[i-1], converted_words[i]
i = 0
x = 0
else
i = i + 1
end
end
end
puts converted_words.to_s

Answer 1

Your code does not "freeze"; running it raises this exception:
NoMethodError (undefined method '<' for nil:NilClass)
in the line:
if converted_words[i][x] < converted_words[i-1][x]
We immediately see the problem, though the cause is not yet known. The receiver of the method < is converted_words[i][x]. As the error message says that nil does not have a method <, we infer that converted_words[i][x] is nil.1 That means that an index is out-of-range (examples of an index being out-of-range are [1,2][412] #=> nil and [1,2][-3] #=> nil). If i were out-of-range the expression would reduce to nil[x] < ..., which would raise an exception that nil does not have a method NilClass#\[\]]. That's not our exception message so we conclude that x must be out-of-range.
To see why this is happening, suppose:
words = ["a", "ab"]
Then
converted_words =
words.map(&:chars).map { |letters| letters.map { |letter| letter.to_i 36 } }
#=> [[10], [10, 11]]
i = 1
x = 0
while i < converted_words.length
#=> while 1 < 2 => while true, so enter the loop
if converted_words[i][x] == converted_words[i-1][x]
#=> if converted_words[1][0] == converted_words[0][0] => if 10 == 10 => true
so execute
x = x + 1
#=> x = 0 + 1 => 1
and attempt to repeat the loop.
while i < converted_words.length
#=> while 1 < 2 => while true, so repeat the loop
if converted_words[i][x] == converted_words[i-1][x]
#=> if converted_words[1][1] == converted_words[0][1] => if 11 == nil => false
so execute (else).
if converted_words[i][x] < converted_words[i-1][x]
#=> converted_words[0][1] < converted_words[-1][1] => if nil < 11
#=> NoMethodError (undefined method '<' for nil:NilClass)
Error messages contain valuable information. Study them carefully!
1 The error message "nil has no method <" is here equivalent to, "NilClass has no instance method <".

Answer 2

I believe I have solved the issue. Thank you for all your help.
I reordered my algorithm: First checking if converted_words[i][x] < converted_words[i-1][x], and then checking if converted_words[i][x] == converted_words[i-1][x].
I also need to check whether if converted_words[i][x] != nil && converted_words[i-1][x] != nil, in order to avoid a NoMethodError (thanks Cary Swoveland).
Finally I combined the two algorithms.
I also realized that I did not need to convert the letters to numbers, as ruby knows which letters are larger. So instead, I left the characters as letters.
I'm aware that the code is not very efficent. If you have any suggestions on how to improve or simplify the algorithm, I would be happy to hear them.
Here's the code:
words = ["my","favorite","animals", "are", "the", "elephant", "and", "the", "antelope", "and", "the", "favela"]
puts words.to_s
#Convert all letters into numbers. Output individual words as arrays.
ordered_words = words.map(&:chars).map { |letters| letters.map { |letter| letter } }
i = 1
x = 0
while i < ordered_words.length
if ordered_words[i][x] != nil && ordered_words[i-1][x] != nil
if ordered_words[i][x] < ordered_words[i-1][x]
ordered_words[i], ordered_words[i-1] = ordered_words[i-1], ordered_words[i]
i = 1
x = 0
else
if ordered_words[i][x] == ordered_words[i-1][x]
x = x + 1
else
i = i + 1
x = 0
end
end
else
if ordered_words[i][x] == nil && ordered_words[i-1][x] == nil
i = i + 1
x = 0
else
if ordered_words[i][x] == nil
ordered_words[i], ordered_words[i-1] = ordered_words[i-1], ordered_words[i]
i = 1
x = 0
else
i = i + 1
x = 0
end
end
end
end
joined_words = []
ordered_words.each do |word|
joined_words.push(word.join)
end
puts joined_words.to_s