Sorting by hash values inside an array of hashes

Question

Im trying to return a list of values inside of of an array of hashes from lowest to highest. I am using the google_drive gem to pull numbers from a google spreadsheet, displaying football information:

Here is where I'm at:

require 'rubygems'
require 'google_drive'

session = GoogleDrive.login("EMAIL", "PASS")




v_qb_w1 =  session.spreadsheet_by_key("xxxxxxxx").worksheets[0]

@quarterbacks = [ 

                { name: v_qb_w1[2, 1], projection: v_qb_w1[2, 2], salary: v_qb_w1[2, 3], dpp: v_qb_w1[2, 4], ppd: v_qb_w1[2, 5] },
                { name: v_qb_w1[3, 1], projection: v_qb_w1[3, 2], salary: v_qb_w1[3, 3], dpp: v_qb_w1[3, 4], ppd: v_qb_w1[3, 5] }, 
                { name: v_qb_w1[4, 1], projection: v_qb_w1[4, 2], salary: v_qb_w1[4, 3], dpp: v_qb_w1[4, 4], ppd: v_qb_w1[4, 5] }
                                      ]

puts "Value:"
@quarterbacks.sort_by do |key, value| 
 dpp = []
 dpp << key[:dpp].to_f.to_s
 puts dpp.flatten.sort.reverse
end

That last block was just one of my attempts to try and sort the :dpp key value from lowest to highest. Nothing fails, it just does not change anything. I've tried the grouby_by method and just have no luck arranging my key values

SOLUTION:

@quarterbacks.sort_by! { |qb| qb[:dpp] }
@quarterbacks.each { |qb| puts qb[:dpp] }

Answer 1

Try this

@quarterbacks.sort_by!{|qb| qb[:dpp]}

You are trying to sort an Array . Right now you passing a Hash (k) and nil (v) because each quarterback is stored as a Hash so there is no key => value association in the Array . Also puts will return nil so you are telling it to sort nil against nil repetitively.

The code above will sort the Array of Hash es by the :dpp attribute of each Hash which seems like what you are asking for. The ! in this case means it will alter the receiver altering the @quarterbacks instance variable to be sorted in place.

Answer 2

First of all, sort_by returns the sorted list, it doesn't sort it in place. That means that just:

@quarterbacks.sort_by { ... }

doesn't do anything useful as you're throwing away the sorted results. You'd need to add an assignment or use sort_by! :

@quarterbacks = @quarterbacks.sort_by { ... }
# or
@quarterbacks.sort_by! { ... }

Then you have understand how the sort_by block works. sort_by sorts using the block's return value, it is more or less like this:

array.map  { |e| [ sort_by_block_value[e], e ] }
     .sort { |a, b| a.first <=> b.first }
     .map  { |e| e.last }

so your block needs to return something sensible rather than the nil that puts returns:

@quarterbacks.sort_by! { |q| q[:dpp] }