How to count values in a array of hashes

Question

I have an array of hashes

[ {:name => "bob", :type => "some", :product => "apples"},
  {:name => "ted", :type => "other", :product => "apples"},.... 
  {:name => "Will", :type => "none", :product => "oranges"} ]

and was wondering if there is a simple way to count the number of product's and store the count as well as the value in an array or hash.

I want the result to be something like:

@products =  [{"apples" => 2, "oranges => 1", ...}]

As per your need, I don't see any reason to keep the hash inside the Array. Is there any reason, then tell us. — Arup Rakshit, Jul 25 '14 at 03:37
Your expected result is not valid. It is impossible to get that. — sawa, Jul 25 '14 at 06:04

score 9 · Accepted Answer · answered Jul 25 '14 at 03:36

9

You can do as

array = [
  {:name => "bob", :type => "some", :product => "apples"},
  {:name => "ted", :type => "other", :product => "apples"},
  {:name => "Will", :type => "none", :product => "oranges"} 
]

array.each_with_object(Hash.new(0)) { |h1, h2| h2[h1[:product]] += 1 }
# => {"apples"=>2, "oranges"=>1}

answered Jul 25 '14 at 03:36

Arup Rakshit

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Thank you for helping me. I knew there was a way to do this easily in Ruby. I tried using inject but had no success. Thank you :) – user2980830 Jul 25 '14 at 03:48
1

for inject, try `array.inject(Hash.new(0)) { |hash, item| hash[item[:product]] += 1; hash }` – jvnill Jul 25 '14 at 03:57
@user2980830 Read *jvnil's* comment. – Arup Rakshit Jul 25 '14 at 03:59
Thanks, is there any advantage of using inject vs. each_with_object? I see they will produce the same result. – user2980830 Jul 25 '14 at 04:01
here's a good explanation from @sawa http://stackoverflow.com/questions/5481009/why-is-enumerableeach-with-object-deprecated/5481396#5481396 – jvnill Jul 25 '14 at 04:21

score 2 · Answer 2 · edited Jan 29 '18 at 09:08

2

You can use Enumerable#group_by and Enumerable#map

array.group_by{|h| h[:product]}.map{|k,v| [k, v.size]}.to_h
# => {"apples"=>2, "oranges"=>1}

edited Jan 29 '18 at 09:08

nrmb

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answered Jul 25 '14 at 05:36

Santhosh

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score 2 · Answer 3 · answered May 25 '18 at 21:21

While not exactly what the OP was looking for, this may be helpful to many. If you're just looking for the count of a specific product, you could do this:

array = [
  {:name => "bob", :type => "some", :product => "apples"},
  {:name => "ted", :type => "other", :product => "apples"},
  {:name => "Will", :type => "none", :product => "oranges"} 
]

array.count { |h| h[:product] == 'apples' }
# => 2

ichigolas · Answer 4 · 2014-07-25T04:21:05.937

0

You could count:

hashes = [
  {:name => "bob", :type => "some", :product => "apples"},
  {:name => "ted", :type => "other", :product => "apples"},
  {:name => "Will", :type => "none", :product => "oranges"}
]

hashes.inject(Hash.new(0)) { |h,o| h[o[:product]] += 1; h }

Or maybe...

hashes.instance_eval { Hash[keys.map { |k| [k,count(k)] }] }

I do not know which is the more performant, the latter seims weird to read though.

edited Jul 25 '14 at 04:21

answered Jul 25 '14 at 03:42

ichigolas

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Can you try the code you have given in IRB? `hashes.inject(Hash.new(0)) { |h,(_,value)| h[value] += 1 }`.. It is completely wrong. – Arup Rakshit Jul 25 '14 at 03:44
I was trying to use inject as i have used it before to count items but have never seen this "(_,value)", thanks for your response – user2980830 Jul 25 '14 at 03:46

score 0 · Answer 5 · answered Jul 25 '14 at 07:52

I would do:

items =[ {:name => "bob", :type => "some", :product => "apples"},
  {:name => "ted", :type => "other", :product => "apples"},
  {:name => "Will", :type => "none", :product => "oranges"} ]

 counts = items.group_by{|x|x[:product]}.map{|x,y|[x,y.count]}
 p counts #=> [["apples", 2], ["oranges", 1]]

Then if you need it as a Hash just do:

 Hash[counts]

How to count values in a array of hashes

5 Answers5