Simple sort in Ruby without using sort method (note that the list to be sorted is "strings")

Question

Given

30.02 -88.87 10.58 -99.22 107.33

to sort without the sort method. I have spent a few hours on this without any success.

def simple_sort(list)      # I have to start with this method

 list = list.split(' ')  # I understand i need to .split to get arrays

Because they're floats I need a way to make them floats with to_f method .each(&:to_f) I saw this before but I'm not sure I understand the ":". I thought colon made objects symbols so anyone please explain (&:to_f) to me?

 sorted_list = []        #thought of creating an empty array to store the new list

This is the part that gets tricky! Where do I go from here?

I want to go through each item in the array, find the smallest number and add it to the sorted_list

def sort_list(list)
  list = list.split(' ').map(&:to_f)
  sort = []
  while sort.length < list.length
    sort << list.min
    list.delete(list.min)
  end
  sort = sort.join(' ')
  return sort
end

instead of using the <=>, what would make this code work?

I have read algorithms for bubble sort, insertion sort, I kinda understand the concept, but lacking the creativity for the method. — Diego, Oct 09 '14 at 17:19
`each(&:to_f)` does nothing useful. It's equivalent to `each { |i| i.to_f }` which simply converts the values to floating point numbers, then discards the results. If you want to save the result, use `map`. — tadman, Oct 09 '14 at 17:23
so when i run this code it gives me the first 3 items in the array as it becomes equal to the length n the list. and stops. — Diego, Oct 09 '14 at 19:05

score 3 · Answer 1 · edited May 23 '17 at 12:05

Open IRB and try things:

>> foo = '30.02 -88.87 10.58 -99.22 107.33'
"30.02 -88.87 10.58 -99.22 107.33"
>> foo.split
[
    [0] "30.02",
    [1] "-88.87",
    [2] "10.58",
    [3] "-99.22",
    [4] "107.33"
]

So split breaks the string on whitespace, so far so good.

>> foo.split.each(&:to_f)
[
    [0] "30.02",
    [1] "-88.87",
    [2] "10.58",
    [3] "-99.22",
    [4] "107.33"
]

Hmm... the values didn't change so each might not be doing what you think it does. Trying map instead:

>> foo.split.map(&:to_f)
[
    [0] 30.02,
    [1] -88.87,
    [2] 10.58,
    [3] -99.22,
    [4] 107.33
]

Once the values are converted to floats then it becomes easy to sort them.

Note: You can use the <=> operator (AKA "spaceship") to tell you whether one is less-than, equal, or greater-than another, which makes it easy to know when you should swap them. For instance:

0 <=> 1 # => -1
1 <=> 1 # => 0
2 <=> 1 # => 1

You should read the documentation for the Comparable module, which makes it really easy to add additional functionally to a class by defining the <=>(other) method.

map allows us to modify/transform an array's elements, whereas each only iterates over them. You can use each to mess with the elements, but it's not generally what you want to do since map! makes it easier to transform things.

Regarding &:to_f. This was a hack on Ruby's symbols a while back, that was added to Rails. It turned out to be so useful that it was pulled into Ruby itself. It's called a "symbol to proc" and is discussed in "Ruby ampersand colon shortcut".

ah I'm trying to post it like its code and as you can see I'm having a hard time there too — Diego, Oct 09 '14 at 18:45
i tried that but I'm getting the first 3 and the rest isn't being << inside sort. — Diego, Oct 09 '14 at 18:46
One of the best written explanations I have seen in a while. — engineersmnky, Oct 09 '14 at 20:12

Simple sort in Ruby without using sort method (note that the list to be sorted is "strings")

1 Answers1