FAQ
Hi,

I am new to programming and following Chris Pines book. There is an
exercise in the book to write a method similar to .sort that will
arrange an array of string in alphabetical order. I will paste the
exercise:

OK. So we want to sort an array of words, and we know how to find out
which of two words comes first in the dictionary (using <).
What strikes me as probably the easiest way to do this is to keep two
more lists around: one will be our list of already-sorted words, and
the
other will be our list of still-unsorted words. We’ll take our list of
words,
find the “smallest” word (that is, the word that would come first in
the
dictionary), and stick it at the end of the already-sorted list. All
of the
other words go into the still-unsorted list. Then you do the same
thing
find
the smallest word, move it to the sorted list, and move the rest to
the
unsorted list. Keep going until your still-unsorted list is empty.

I think I covered the first bit of the exercise but when I try to
repeat my method recursively it fails.
Would you be please so kind to take a look at my code and tell me what
am I doing wrong?

puts 'Please enter a list of words you would like to arrange'
puts 'in alphabetical order:'

list_of_words = []
input = 'empty'

while input != ''
input = gets.chomp
if input != ''
list_of_words.push input
end
end

def arrange some_array
recursive_arrange some_array, []
end

def recursive_arrange unsorted_array, sorted_array

# Initializing the array "still_unsorted_array"

still_unsorted_array = []

# Finding the smallest word on the array "list_of_words"

smallest = unsorted_array [0]

unsorted_array.each do |word|
if smallest > word
smallest = word
end
end

# Adding the smallest word from the array of "unsorted words" to the
array of "sorted_words"

sorted_array.push smallest

# Adding the words from the array of "unsorted_array" to the array of
"still_unsorted_array"
# with the exception of the content of variable "smallest"

bigger = 'empty'

unsorted_array.each do |word|
if word != smallest
bigger = word
still_unsorted_array.push bigger
end
end

# Clearing the array of "unsorted_array" so it can be re-used

unsorted_array = []
# Adding the smallest word from the array of "still_unsorted words" to
the array of "sorted_words"

smallest = still_unsorted_array [0]
still_unsorted_array.each do |word|
if smallest > word
smallest = word
end
end

# Adding the smallest word from the array of "still_unsorted words" to
the array of "sorted_words"

sorted_array.push smallest

# Adding the remaining words from the array "still_unsorted_words" to
the array of
# "unsorted_words"

still_unsorted_array.each do |word|
if word != smallest
bigger = word
unsorted_array.push bigger
end
end

# This is the bit I tried to call the method recursively.

if unsorted_array == unsorted_array = []
puts sorted_array
else
recursive_arrange unsorted_array, sorted_array
end

puts 'unsorted array:'
puts unsorted_array
puts 'still unsorted array:'
puts still_unsorted_array
puts 'sorted array:'
puts sorted_array

end

arrange list_of_words

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## Search Discussions

•  at Jan 19, 2012 at 6:22 pm ⇧

On Jan 19, 2012, at 10:39 AM, Loren wrote:

Would you be please so kind to take a look at my code and tell me what
am I doing wrong?
You're making this far, far, far more complicated than it needs to be. Hint 1: you only need two arrays, sorted & unsorted, all the shuffling in & out of temporary arrays is unnecessary and just complicates your code--this is by far most important. Hint 2: use the appropriate functions on enumerable (parent class of array) with blocks to get rid of the loops--maybe your book hasn't gotten to this yet, if so don't worry about it, but it's those functions that let you express the sorting part in about 10 lines or so of code.

--
Scott Ribe
scott_ribe@elevated-dev.com
http://www.elevated-dev.com/
(303) 722-0567 voice

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 group rubyonrails-talk categories rubyonrails posted Jan 19, '12 at 5:39p active Jan 19, '12 at 6:22p posts 2 users 2 website rubyonrails.org irc #RubyOnRails

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