Ruby profiler results interpretation - ruby

Question

I'm using a ruby-prof gem to profile my code.
And results looks like this:
%self total self wait child calls name
50.56 31.06 23.45 0.00 7.62 234593 Array#each
14.29 6.62 6.62 0.00 0.00 562480 Array#-
13.63 6.32 6.32 0.00 0.00 157816 Array#|
11.20 5.20 5.20 0.00 0.00 6210903 Hash#default
2.44 46.36 1.13 0.00 46.36 78909 Analyzer#process
2.02 46.36 0.94 0.00 46.36 78908 Analyzer#try
1.70 0.79 0.79 0.00 0.00 562481 UnboundMethod#bind
1.53 7.34 0.71 0.00 6.62 562480 Method#call
1.18 0.55 0.55 0.00 0.00 562480 Kernel#instance_variable_defined?
0.76 46.36 0.35 0.00 46.36 6250 Array#combination
0.37 0.17 0.17 0.00 0.00 105763 Array#concat
0.25 25.19 0.12 0.00 25.07 77842 Enumerable#group_by
0.02 46.36 0.01 0.00 46.36 3125 Enumerator#each
0.02 0.01 0.01 0.00 0.00 78908 Array#empty?
...
I'm sure that my code does not tries to access non-existing keys in some of the Hashes.
The question is - what Hash#default might mean?
And here is a piece of code:
class Analyzer
def process(level, hypo_right, hypo_wrong)
if portion = #portions[level]
selections = #selections[level] - hypo_wrong
master_size = selections.size
selections -= hypo_right
new_portion = portion + selections.size - master_size
if new_portion > selections.size || new_portion < 0
return
elsif new_portion == 0
try(level, hypo_right, [], hypo_wrong, selections)
else
selections.combination(new_portion).each do |hypo_right2|
try(level, hypo_right, hypo_right2, hypo_wrong, (selections - hypo_right2))
end
end
else
puts hypo_right.inspect
end
end
def try(level, right, right2, wrong, wrong2)
local_right = right | right2
local_wrong = wrong | wrong2
right2.each { |r| local_wrong.concat(#siblings[r]) }
unless wrong2.empty?
grouped_wrong = local_wrong.group_by{|e| #vars[e] }
wrong2.each do |w|
qid = #vars[w]
if grouped_wrong[qid].size == #limits[qid]
local_right << (#q_hash[qid] - grouped_wrong[qid])[0]
end
end
end
process(level + 1, local_right, local_wrong)
end
def start
process(0, [], [])
end
end
#selections, #portions are Arrays; #q_hash, #siblings, #limits and #vars are Hashes.

Answer 1

Thanks to riffraff, found answer:
require 'ruby-prof'
h = (0..9).inject({}) {|h, x| h[x] = (x+97).chr;h }
a = (0..1000000).collect { rand(100) }
RubyProf.start
g = a.group_by {|x| h[x/10] }
RubyProf::FlatPrinter.new(RubyProf.stop).print(STDOUT)
Thread ID: 17188993880
Total: 1.210938
%self total self wait child calls name
100.00 1.21 1.21 0.00 0.00 1 Array#each
0.00 0.00 0.00 0.00 0.00 10 Hash#default
0.00 1.21 0.00 0.00 1.21 1 Enumerable#group_by
0.00 1.21 0.00 0.00 1.21 1 Object#irb_binding