FAQ: Methods, Blocks, & Sorting - Sorting

This community-built FAQ covers the “Sorting” exercise from the lesson “Methods, Blocks, & Sorting”.

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FAQs on the exercise Sorting

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I need some help with understanding the descending order with combined operator.

Why it will sort it in descending order if I use the {} brackets and not the sort method?

fruits = ["orange", "apple", "banana", "pear", "grapes"]

print fruits.sort! do |b, a|
    a <=> b
end

print fruits.sort! { |b, a| a <=> b }

the result is

["apple", "banana", "grapes", "orange", "pear"]
["pear", "orange", "grapes", "banana", "apple"]

thanks

1 Like

The exercise suggests as an alternative, sorting with an if/else statement. I succeeded with the following:

fruits = ["orange", "apple", "banana", "pear", "grapes"]

fruits.sort! do |fruit1, fruit2|
  if fruit1 <= fruit2
    fruit1 = 1
  else fruit1 = 0
  end
end
  
puts fruits

But I don’t really understand how this works (just as I don’t really understand how it works with <=>) Specifically, I haven’t wrapped my head around how the 2 “comparison values” (fruit1, fruit2) are then applied to an array of more than 2 values. I guess this is about the inner workings of the .sort! method & I’ll probably come to understand it better with time.

1 Like

PS I’m also curious about melina84’s question (#2). Does puts / print only take the block if it’s on a single line? It worked when I modified melina84’s code as follows, running the puts after the sort block.

fruits = ["orange", "apple", "banana", "pear", "grapes"]

fruits.sort! do |b, a|
    a <=> b
end
puts fruits

fruits.sort! {|b, a| a <=> b }
puts fruits

The following use of parentheses also works, and seems to kinda support my theory:

puts (
  fruits.sort! do |b, a|
    a <=> b
  end
  )
1 Like

Also curious how fruitTwo <=> fruitOne can be applied to this array since this array has 5 fruits (not 2).

3 Likes

Will it be because of the “Do” statement kind of a while loop it will do it until all of the iterations are evaluated?

same as above comments. Why did the block method not work but curly braces worked?

Hi everyone,

I know the point of the exercise might have just been to teach us <=>
I’m wondering if anyone can explain why we would want to use the curly braces at all when fruits.sort! sorts it alphabetically, and then fruits.reverse! reverses it. Nothing extra needed. I’m just looking for some context to it :slightly_smiling_face:
Thanks!

fruits = ["orange", "apple", "banana", "pear", "grapes"]

fruits1 = ["orange", "apple", "banana", "pear", "grapes"]

fruits.sort!
fruits.reverse!
fruits.each {|x| puts x}

puts ""

fruits1.sort! do |firstFruit, secondFruit|
  secondFruit <=> firstFruit
end
fruits1.each {|x| puts x}

Hi p0nd3r,

I believe, rereading the instructions/explanation on the “Foundations” exercise (13/19) and “The Combined Comparison Operator” (14/19), the answer to your question about 2 values compared in an array of more than 2 values has to do with how the algorithms work. From my understanding, I believe the .sort! method is comparing each of the values in the array to each of the others. So for each comparison that it runs, there are two values being compared. The algorithm doesn’t compare all 5 values at once, but two at a time.

So for each of those comparison that it runs, we’re telling it how to compare those two items. In order to do this, we are calling the two values being compared at each given step fruit1 and fruit2.

Crazy that they dropped “Try it with an if/else statement!” in there without any guidance or an example of the correct answer. That’s what I came to the forums to find. Thanks for posting yours.

1 Like

Please see my reply to p0nd3r for my best explanation.

[FAQ: Methods, Blocks, & Sorting - Sorting - #9 by jessebrooks309491380]

For the following code:

fruits.sort! { |fruit1, fruit2|
if fruit1 > fruit2
-1
elsif fruit1 < fruit2
1
else
0
end
}
puts fruits

does this mean:
if fruit 1 comes after fruit 2 alphabetically, put it before.
elsif fruit 2 comes before fruit 1 alphabetically, but it after.
else when they are the same word then they can appear either before or after the other

If so, that means -1 is indicating what should come first
But doesn’t that contradict what we saw in the beginning of this lesson:

def capitalize(string)
puts “#{string[0].upcase}#{string[1…-1]}”
end

The -1 here indicated the last element

How does that make sense? Or am I misunderstanding? Can someone please help clarify this?