Ruby String sorting method

Question

I am trying to get some clarification on why one line of code passes an rspec test and another does not. I was tasked with writing a method that sorted an array of strings by length. I tried to different sort options with different blocks be passed into the sort method. I think I may have figure it out in my comments on my code.

Does my commented out line of code not pass the test because it is literally only checking the length of a new item each time a new item is passed into the block instead of checking the length of an item against the lengths of the other items in the array of strings defined in the spec. If that makes sense..

My code is as follows:

def sort_by_length(sort_this_array)
   #sort_this_array.sort {|item| item.length }
    sort_this_array.sort {|x,y| x.length <=> y.length }
end

The RSpec is as follows:

describe "sort_by_length" do
  it "sorts an array of strings by length" do
    a = %w(z yyyy xxx ww)
    sorted = %w(z ww xxx yyyy)
    expect( sort_by_length(a) ).to eq(sorted)
  end
  it "sorts hashes by length" do
    a = [{a: "a", b: "b"}, { key: "value"}, {}]
    sorted = [{}, { key: "value"}, {a: "a", b: "b"}]
    expect( sort_by_length(a) ).to eq(sorted)
  end
end

    describe "sort_by_length" do
  it "sorts an array of strings by length" do
    a = %w(z yyyy xxx ww)
    sorted = %w(z ww xxx yyyy)
    expect( sort_by_length(a) ).to eq(sorted)
  end
  it "sorts hashes by length" do
    a = [{a: "a", b: "b"}, { key: "value"}, {}]
    sorted = [{}, { key: "value"}, {a: "a", b: "b"}]
    expect( sort_by_length(a) ).to eq(sorted)
  end
end

Mischa · Accepted Answer · 2015-09-28 03:51:45Z

2

When using sort you always have to compare two variables and return -1, 0 or 1. From the documentation:

The block must implement a comparison between a and b, and return -1, when a follows b, 0 when a and b are equivalent, or +1 if b follows a.

In your commented out line you're not doing that. If you use sort_by, you can use that syntax:

 array.sort_by { |item| item.length }

edited Sep 28, 2015 at 3:51

answered Sep 28, 2015 at 2:09

Mischa

43.4k9 gold badges101 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Amadan Over a year ago

Note also that sort_by is faster, since it only evaluates item.length once per item (n times); sort will evaluate item.length twice per comparison (so, around 2*n*log(n) times). You should only use sort if the comparator function is complex. And further, note that you can write this specific case even more concisely as array.sort_by(&:length).

Collectives™ on Stack Overflow

Ruby String sorting method

The RSpec is as follows:

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

The RSpec is as follows:

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related