Separating array with different objects into specific object arrays in ruby

Question

Imagine I have an array with different types of objects such as:

[1,true,'hello',true,2,' ','world']

I'm trying to create a function that outputs an array of arrays with those objects separated.

[ [1,2] , ['hello', ' ', 'world'] , [true,true] ]

So far i've come with this:

def same_object arg
    arg.inject([]){ |acc,value| 
            flag = 0
            acc.each do |i|
                if i[0] != nil && value.class == i[0].class
                    i << value
                    flag = 1
                end
            end

            if flag == 0
                acc << [value]
            end
    }
end

The problem is that apparently I get an error when I do:

value.class == i[0].class

Which is kind of weird, because for me it makes sense. I'm new to ruby and I'd appreciate some insight.

spickermann · Accepted Answer · 2015-03-17 12:11:12Z

5

Your example fails, because you do not return updated acc at the end of the inject block. Just add acc before the closing }:

  #...
  end
  acc
}

Beside that I would do something like this:

[1,true,'hello',true,2,' ','world'].group_by(&:class).values
#=> [[1, 2], [true, true], ["hello", " ", "world"]]

edited Mar 17, 2015 at 12:11

answered Mar 17, 2015 at 12:01

spickermann

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6 Comments

Manoel Ribeiro Over a year ago

Do you have any clue why this goes wrong inside mine? Your answer is pretty awesome anyways : )

Manoel Ribeiro Over a year ago

undefined method each' for nil:NilClass from singlefile.rb:48:in block in same_object' from singlefile.rb:46:in each' from singlefile.rb:46:in inject' from singlefile.rb:46:in `same_object'

Manoel Ribeiro Over a year ago

what I think is weird is that i'm checking for the nil class, so it shouldn't fail :/

PinnyM Over a year ago

@ManoelRibeiro You need to have acc returned as the last line of your block. Without this, it will return nil to the next cycle of inject in the case that flag != 0.

PinnyM Over a year ago

Because that's how inject works :) The accumulator/memo object (acc for your case) starts off as nil or as the passed in object ([] in your case) and for each consecutive pass it is the result returned by the block on the previous pass. This method is commonly called reduce in other languages (also aliased as such in ruby). Have a look at the Enumerable#each_with_object method that may be more in line with what you are expecting.

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