5
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I'm trying to optimize this bit of code and I thought I'd throw it out here to see if anyone has any ideas. I've been testing the performance using Benchmark.measure {...} and wrapping the entire function.

Yes, the item has a date that is a Ruby Date

  puts Benchmark.measure {
    grouped_items
  }

  def grouped_items
    unless @grouped
      @grouped = {}
      @items.each do |item|
        key = item.date
        if @grouped.has_key?(key)
          @grouped[key] << item
        else
          @grouped[key] = [item]
        end
      end
    end
    @grouped
  end

Thanks for any insight you care to share.

Edit #1: My first optimization. I was aiming for a slightly more succinct function and gained a .2 seconds reduction in time to process 100_000 items.

  def grouped_items
    unless @grouped
      @grouped = Hash.new { |h, k| h[k] = [] }
      @items.map {|item| @grouped[item.date] << item }
    end
    @grouped
  end

Edit #2: My second iteration with more or less the same performance profile but with much less code.

def grouped_items
  @grouped ||= @items.group_by { |item| item.date }
end

Edit #3: An alternative way to do the same thing above.

def grouped_items
  @grouped ||= @items.group_by &:date
end
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3
  • \$\begingroup\$ Nope. I'll check that out. \$\endgroup\$ Commented Jul 7, 2012 at 1:21
  • \$\begingroup\$ In future can you flag for a mod to migrate, please don't cross-post. Thanks. \$\endgroup\$
    – Kev
    Commented Jul 8, 2012 at 0:58
  • \$\begingroup\$ Did you try profiling the code? \$\endgroup\$ Commented Jul 12, 2012 at 2:41

2 Answers 2

8
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Are you aware of Enumerable#group_by?

def grouped_items
  @items.group_by{|item| item.date}
end
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4
  • \$\begingroup\$ It more or less performs the same as the first edit (see above) but with much less code. \$\endgroup\$ Commented Jul 7, 2012 at 1:44
  • 1
    \$\begingroup\$ I just came back across this and wanted to comment again how awesome this solution is. :) \$\endgroup\$ Commented Jul 29, 2012 at 17:44
  • \$\begingroup\$ Just to add, you could even use symbol-to-proc here since you are grouping by an immediate method call: @items.group_by &:date. \$\endgroup\$ Commented Dec 16, 2014 at 9:39
  • \$\begingroup\$ Indeed, as the OP discovered and showed in his Edit #3. \$\endgroup\$ Commented Dec 16, 2014 at 14:24
4
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What about this?

@items.group_by { |item| item.effective_date }

Benchmarks for the curious:

Ryan v1 : 1.080000   0.000000   1.080000 (  1.077599)
Ryan v2 : 0.620000   0.000000   0.620000 (  0.622756)
group_by: 0.580000   0.000000   0.580000 (  0.576531)
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