Array.count with block does not return correct answer

Question

I have an array of Assignment objects that I create from a database call:

@assignments = @player.assignments

I want to count them with this:

@assignments.count {|x| x.sets == 0.0}

This should count the number of assignments with 0.0 sets. However, this always returns the total number of objects in @assignments. I have checked that

@assignments.each {|x| puts x.sets == 0.0}

does not return true in all the cases. Any clues?

Edit>

@assignments.map(&:sets)
=> [35.0, 120.0, 0.0, 0.0, 0.0, 0.0, 0.0, 12.0, 75.0, 0.0, 0.0, 0.0, 0.0]

It works for me [1] pry(main)> assignments = [35.0, 120.0, 0.0, 0.0, 0.0, 0.0, 0.0, 12.0, 75.0, 0.0, 0.0, 0.0, 0.0] => [35.0, 120.0, 0.0, 0.0, 0.0, 0.0, 0.0, 12.0, 75.0, 0.0, 0.0, 0.0, 0.0] [2] pry(main)> assignments.count {|x| x == 0.0} => 9 [3] pry(main)> assignments.count => 13 — Karthik T
– Karthik T, Commented Aug 19, 2013 at 8:35
This works for me too a = [35.0, 120.0, 0.0, 0.0, 0.0, 0.0, 0.0, 12.0, 75.0, 0.0, 0.0, 0.0, 0.0] => [35.0, 120.0, 0.0, 0.0, 0.0, 0.0, 0.0, 12.0, 75.0, 0.0, 0.0, 0.0, 0.0] a.count {|x| x == 0.0} => 9 — Andreas Lyngstad
– Andreas Lyngstad, Commented Aug 19, 2013 at 8:35

you786 · Accepted Answer · 2017-12-13 19:10:23Z

27

Most likely, @assignments is not an Array instance, but ActiveRecord::Relation, try @assignments.class. If so, count method does not work as you expected, it returns numbers of records.

Try

@assignments.where(sets: 0).count

Or even (convert to array first)

@assignments.to_a.count {|x| x.sets == 0.0}

edited Dec 13, 2017 at 19:10

you786

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answered Aug 19, 2013 at 8:39

dimuch

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5 Comments

user1742188 Over a year ago

It is returned by a Rails ActiveRecord method. But @assignments.class returns Array. But your solution worked for me, so I guess it is as you say. Thank you very much!

tokland Over a year ago

@user1742188: Rails 2? It may say "Array" but it's not a plain array. One of the innumerable hacks that fortunately are being solved in latests versions.

user1742188 Over a year ago

Its Rails 3.2.8. Gah. Thanks for the info tokland. This was seriously crazy. The documentation should note such exceptions.

tokland Over a year ago

@user1742188: Paste in the question how you create @assignments. That Array thing is documented somewhere.

DylanReile Over a year ago

.all was still returning ActiveRecord::Relation for me. I had to use .all.to_a.

Rails Guy · Accepted Answer · 2013-08-19 08:30:52Z

2

Try with this:

    @assignments.select {|x| x if x.sets == 0.0}.count

Thanks

answered Aug 19, 2013 at 8:30

Rails Guy

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2 Comments

singularity Over a year ago

This answer works for when you want to use a method to return the count. Meaning, if you're not counting based on an object's attribute, but rather based on a method. For instance: people.select {|person| person if person.tall?}.count

max pleaner Over a year ago

@singularity .select(<block>).count is really the same as count(<block>), just a little more verbose.

dirtydexter · Accepted Answer · 2013-08-19 08:59:57Z

0

see count or each just count the number of objects only(internally it checks for each object as if object will be present it will return true if its nill will return false, so actually it counts the number of true that are returned by the block), if you want to count the number of times your condition holds true i suggest you try using the inject iterator that is made for these type of computations only in the ruby.

It will be like this

@assignments.inject(0) {|sum,x| 
  if x.sets == 0.0
    sum + 1
  else
    sum
  end
}

edited Aug 19, 2013 at 8:59

answered Aug 19, 2013 at 8:31

dirtydexter

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3 Comments

Karthik T Over a year ago

not true, atleast for ruby's count

dirtydexter Over a year ago

@user1742188 will you try this one too once.

Karthik T Over a year ago

In that case you should edit your answer accordingly, since as I say, the default count works exactly as OP wants it to

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