Count class instances in array

Question

I have rails app with models Car and Wheel. And I have the method which returns an array of different objects. e.g.

array = [Car.new, Car.new, Wheel.new, Wheel.new, 'home', 'market', 'fun']

How to count Car instances and Wheel instances in an array?

I tried array.include?(Car) and array.count(Car) and they didn't work.

score 7 · Accepted Answer · answered Oct 17 '16 at 07:56

7

You can use Enumerable#grep to fetch the instances of Car:

array.grep(Car).size

answered Oct 17 '16 at 07:56

ndnenkov

`Enumerable#grep` is definitely undervalued, love it! – Aleksei Matiushkin Oct 17 '16 at 09:49
I have to say that this is really a great way. – Sajan Oct 17 '16 at 09:49

score 2 · Answer 2 · answered Oct 17 '16 at 07:45

2

you can do like below for counting Car instance:

array.count { |e| e.instance_of? Car}

or instead of instance_of? you can use kind_of? if that sounds better.

answered Oct 17 '16 at 07:45

Sajan

score 2 · Answer 3 · edited May 23 '17 at 12:30

2

kind_of? and is_a? are synonymous. They are Ruby's equivalent to Java's instanceof.

instance_of? is different in that it only returns true if the object is an instance of that exact class, not a subclass

array.count { |e| e.instance_of? Car}

edited May 23 '17 at 12:30

Community

answered Oct 17 '16 at 07:53

Gagan Gami

3 Answers3