Ruby hashes of status counts

Question

I have a method that takes a model object, reads through its children and returns a hash of status counts. It should only return a count on a status if one exists.

This method works, but I was wondering if there are a cleaner, more Rubyish way to write it.

The batch_details table is getting very large, so if possible I'd like not to access it twice.

def batch_status
 batch_status = {
 'ready' => 0,
 'processing' => 0,
 'error' => 0,
 'purchase' => 0,
 'completed' => 0
 }
 self.batch_details.each do |bd|
 batch_status[bd.status] = batch_status[bd.status] + 1
 end 
 batch_status['count'] = self.batch_details.count
 batch_status.delete_if {|k, v| v == 0 }
 return batch_status
end
2.1.2 :002 > b.batch_status
 => {"completed"=>4, "count"=>4} 

Answer 1

You can use Array#group_by to produce a hash keyed by status. Then follow that by a map to collect the counts. You'll get an array of key/value pairs, so use Hash[] to make that into a proper hash:

def batch_status
 counts = self.batch_details.group_by(&:status).map { |k, v| [k, v.count] }
 Hash[counts]
end

Alternatively, you can use use your current approach, just shortened a bit

def batch_status
 self.batch_details.reduce({}) do |counts, details|
 counts[details.status] = (counts[details.status] || 0) + 1
 end
end

---

Edit: Completely overlooked the "count" key. I muddies the picture a little, but you could do something like this for code blocks 1 and 2 above

def batch_status
 counts = self.batch_details.group_by(&:status).map { |k, v| [k, v.count] }
 counts << ["count", self.batch_details.count]
 Hash[counts]
end

and

def batch_status
 counts = { "count" => self.self.batch_details.count }
 self.batch_details.reduce(counts) do |counts, details|
 counts[details.status] = (counts[details.status] || 0) + 1
 counts
 end
end

Or, as Cary Swoveland suggests:

def batch_status
 counts = { "count" => self.self.batch_details.count }
 counts.default = 0
 self.batch_details.reduce(counts) do |counts, details|
 counts[details.status] += 1
 counts
 end
end

Which cleans it up nicely. Further cleanup could be done by using each_with_object in place of reduce:

def batch_status
 counts = { "count" => self.self.batch_details.count }
 counts.default = 0
 self.batch_details.each_with_object(counts) do |counts, details|
 counts[details.status] += 1
 end
end

• Cary Swoveland: One possible change to your last batch_status--which I think reads quite well--is to add counts.default = 0 after the first line and then use += 1 in the block.
• Flambino: @CarySwoveland Good idea - I'll add that

Answer 2

This is a variant of @Flambino's second suggestion, which starts with an empty hash, to avoid the step of deleting keys whose values are zero.

def batch_status
 self.batch_details.each_with_object(Hash.new(0)) {|bd,h| batch_status[bd.status] += 1}
 .merge({"count"=>self.batch_details.count})
end

• TNT: Missing closing parenthesis after Hash.new(0). Cannot edit...
• Cary Swoveland: Thanks, TNT. I thought I had fixed that, but it's fixed now.