Finally, simple mean, median, mode, sum, and frequencies for Ruby arrays and enumerables!
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README.md

SimpleStats Build Status

Install without Bundler:

gem install simple_stats --no-ri --no-rdoc

Install with Bundler:

gem "simple_stats"

Then get some statistics on arrays or enumerables:

require 'rubygems' # if not using Bundler
require 'simple_stats'

samples = [3, 1, 0, 8, 2, 2, 3, 9]

samples.sum    # 28 
samples.mean   # 3.5 
samples.median # 2.5 
samples.modes  # [2, 3] 
samples.frequencies
# {
#   0 => 1,
#   1 => 1,
#   2 => 2,
#   3 => 2,
#   8 => 1,
#   9 => 1
# }
samples.sorted_frequencies
# most common elements first
# [
#   [2, 2],
#   [3, 2],
#   [0, 1],
#   [1, 1],
#   [8, 1],
#   [9, 1]
# ]

# of course, you can take modes/frequencies on non-numeric data...
"banana nanny!".chars.modes
# ["n"]
"banana nanny!".chars.frequencies
# {
#   " " => 1,
#   "! "=> 1,
#   "a" => 4,
#   "b" => 1,
#   "n" => 5,
#   "y" => 1
# }
"banana nanny!".chars.sorted_frequencies
# [
#   ["n", 5],
#   ["a", 4],
#   [" ", 1],
#   ["!", 1],
#   ["b", 1],
#   ["y", 1]
# ]

# sum of nothing is 0
[].sum # 0

# mean and median of nothing is undefined
[].mean   # nil
[].median # nil

# modes and frequencies return empty containers
[].modes              # []
[].frequencies        # {}
[].sorted_frequencies # []

# if elements are present, mean and median always return floats
[1, 2, 3].mean      # 2.0
[1, 2, 3].median    # 2.0
[1, 2, 3, 4].mean   # 2.5
[1, 2, 3, 4].median # 2.5

# sum, mode, and frequencies preserve the object class
[1, 2, 3].sum       # 6
[1.0, 2.0, 3.0].sum # 6.0

# but no guarantees on class here:
[2.0, 2,   1].modes # [2]
[2,   2.0, 1].modes # [2.0]

Mapping

If the thing you want stats on is buried in your objects, you can pass a block to any SimpleStats method.

# these two lines do the same thing
cities.mean {|city| city.population}
cities.map  {|city| city.population}.mean

# other examples
cities.sum(&:public_school_count)
cities.mean(&:public_school_count)
cities.frequencies(&:professional_team_count)

# more complicated examples
cities.median {|city| city.municipal_income / city.schools.sum(&:students)}
cities.map(&:schools).flatten.modes(&:team_name) # most common school sports team name
cities.map(&:professional_teams).flatten.sorted_frequencies(&:kind) # number of different kinds of sports teams

Interaction with other gems

If any of SimpleStats' methods are already defined on Enumerable, SimpleStats will not replace them with its own definition. In particular, ActiveSupport defines a sum method. If both ActiveSupport and SimpleStats are used, the sum method will come from ActiveSupport. Don't worry, ActiveSupport and SimpleStats should work fine together.

Help make it better!

Need something added? Open an issue. Or, even better, code it yourself and send a pull request:

# fork it on github, then clone:
git clone git@github.com:your_username/simple_stats.git
bundle install
rspec
# hack away
git push
# then make a pull request

License

Public domain. (I, Brian Hempel, the original author release this code to the public domain. February 10, 2012.)