Module: Enumerable

Included in:
Tb, Tb::Record
Defined in:
lib/tb/enumerable.rb

Overview

lib/tb/enumerable.rb - extensions for Enumerable

Copyright © 2010 Tanaka Akira <[email protected]>

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Instance Method Summary collapse

Instance Method Details

#tb_categorize(*args, &reduce_proc) ⇒ Object

:call-seq:

enum.tb_categorize(ksel1, ksel2, ..., vsel, [opts])
enum.tb_categorize(ksel1, ksel2, ..., vsel, [opts]) {|ks, vs| ... }

categorizes the elements in enum and returns a hash. This method assumes multiple elements for a category.

tb_categorize takes one or more key selectors, one value selector and an optional option hash. It also takes an optional block.

The selectors specify how to extract a value from an element in enum.

The key selectors, kselN, are used to extract hash keys from an element. If two or more key selectors are specified, the result hash will be nested.

The value selector, vsel, is used for the values of innermost hashes. By default, all values extracted by vsel from the elements which key selectors extracts same value are composed as an array. The array is set to the values of the innermost hashes. This behavior can be customized by the options: :seed, :op and :update.

a = [{:fruit => "banana", :color => "yellow", :taste => "sweet", :price => 100},
     {:fruit => "melon", :color => "green", :taste => "sweet", :price => 300},
     {:fruit => "grapefruit", :color => "yellow", :taste => "tart", :price => 200}]
p a.tb_categorize(:color, :fruit)
#=> {"yellow"=>["banana", "grapefruit"], "green"=>["melon"]}
p a.tb_categorize(:taste, :fruit)
#=> {"sweet"=>["banana", "melon"], "tart"=>["grapefruit"]}
p a.tb_categorize(:taste, :color, :fruit)
#=> {"sweet"=>{"yellow"=>["banana"], "green"=>["melon"]}, "tart"=>{"yellow"=>["grapefruit"]}}
p a.tb_categorize(:taste, :color)
#=> {"sweet"=>["yellow", "green"], "tart"=>["yellow"]}

In the above example, :fruit, :color and :taste is specified as selectors. There are several types of selectors as follows:

  • object with call method (procedure, etc.): extracts a value from the element by calling the procedure with the element as an argument.

  • array of selectors: make an array which contains the values extracted by the selectors.

  • other object: extracts a value from the element using [] method as element[selector].

So the selector :fruit extracts the value from the element :fruit => “banana”, :color => “yellow”, :taste => “sweet”, :price => 100} as {….

p a.tb_categorize(lambda {|elt| elt[:fruit][4] }, :fruit)
#=> {"n"=>["banana", "melon"], "e"=>["grapefruit"]}

When the key selectors returns same key for two or or more elements, corresponding values extracted by the value selector are combined. By default, all values are collected as an array. :seed, :op and :update option in the option hash customizes this behavior. :seed option and :op option is similar to Enumerable#inject. :seed option specifies an initial value. (If :seed option is not given, the first value for each category is treated as an initial value.) :op option specifies a procedure to combine a seed and an element into a next seed. :update option is same as :op option except it takes three arguments instead of two: keys, seed and element. to_proc method is used to convert :op and :update option to a procedure. So a symbol can be used for them.

# count categorized elements.
p a.tb_categorize(:color, lambda {|e| 1 }, :op=>:+)
#=> {"yellow"=>2, "green"=>1}

p a.tb_categorize(:color, :fruit, :seed=>"", :op=>:+)
#=> {"yellow"=>"bananagrapefruit", "green"=>"melon"}

The default behavior, collecting all values as an array, is implemented as follows.

:seed => nil
:update => {|ks, s, v| !s ? [v] : (s << v) }

:op and :update option are disjoint. ArgumentError is raised if both are specified.

The block for tb_categorize method converts combined values to final innermost hash values.

p a.tb_categorize(:color, :fruit) {|ks, vs| vs.join(",") }
#=> {"yellow"=>"banana,grapefruit", "green"=>"melon"}

# calculates the average price for fruits of each color.
p a.tb_categorize(:color, :price) {|ks, vs| vs.inject(0.0, &:+) / vs.length }
#=> {"yellow"=>150.0, "green"=>300.0}



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# File 'lib/tb/enumerable.rb', line 113

def tb_categorize(*args, &reduce_proc)
  opts = args.last.kind_of?(Hash) ? args.pop : {}
  if args.length < 2
    raise ArgumentError, "needs 2 or more arguments without option hash (but #{args.length})"
  end
  value_selector = tb_cat_selector_proc(args.pop)
  key_selectors = args.map {|a| tb_cat_selector_proc(a) }
  has_seed = opts.include? :seed
  seed_value = opts[:seed]
  if opts.include?(:update) && opts.include?(:op)
    raise ArgumentError, "both :op and :update option specified"
  elsif opts.include? :update
    update_proc = opts[:update].to_proc
  elsif opts.include? :op
    op_proc = opts[:op].to_proc
    update_proc = lambda {|ks, s, v| op_proc.call(s, v) }
  else
    has_seed = true
    seed_value = nil
    update_proc = lambda {|ks, s, v| !s ? [v] : (s << v) }
  end
  result = {}
  each {|*elts|
    elt = elts.length <= 1 ? elts[0] : elts
    ks = key_selectors.map {|ksel| ksel.call(elt) }
    v = value_selector.call(elt)
    h = result
    0.upto(ks.length-2) {|i|
      k = ks[i]
      h[k] = {} if !h.include?(k)
      h = h[k]
    }
    lastk = ks.last
    if !h.include?(lastk)
      if has_seed
        h[lastk] = update_proc.call(ks, seed_value, v)
      else
        h[lastk] = v
      end
    else
      h[lastk] = update_proc.call(ks, h[lastk], v)
    end
  }
  if reduce_proc
    tb_cat_reduce(result, [], key_selectors.length-1, reduce_proc)
  end
  result
end

#tb_category_count(*args) ⇒ Object

:call-seq:

enum.tb_category_count(ksel1, ksel2, ...)

counts elements in enum for each category defined by the key selectors.

a = [{:fruit => "banana", :color => "yellow", :taste => "sweet", :price => 100},
     {:fruit => "melon", :color => "green", :taste => "sweet", :price => 300},
     {:fruit => "grapefruit", :color => "yellow", :taste => "tart", :price => 200}]

p a.tb_category_count(:color)
#=> {"yellow"=>2, "green"=>1}

p a.tb_category_count(:taste)
#=> {"sweet"=>2, "tart"=>1}

p a.tb_category_count(:taste, :color)
#=> {"sweet"=>{"yellow"=>1, "green"=>1}, "tart"=>{"yellow"=>1}}

The selectors specify how to extract a value from an element in enum. See Enumerable#tb_categorize for details of selectors.



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# File 'lib/tb/enumerable.rb', line 280

def tb_category_count(*args)
  tb_categorize(*(args + [lambda {|e| 1 }, {:update => lambda {|ks, s, v| s + v }}]))
end

#tb_unique_categorize(*args, &update_proc) ⇒ Object

:call-seq:

enum.tb_unique_categorize(ksel1, ksel2, ..., vsel, [opts]) -> hash
enum.tb_unique_categorize(ksel1, ksel2, ..., vsel, [opts]) {|s, v| ... } -> hash

categorizes the elements in enum and returns a hash. This method assumes one element for a category by default.

tb_unique_categorize takes one or more key selectors, one value selector and an optional option hash. It also takes an optional block.

The selectors specify how to extract a value from an element in enum. See Enumerable#tb_categorize for details of selectors.

The key selectors, kselN, are used to extract hash keys from an element. If two or more key selectors are specified, the result hash will be nested.

The value selector, vsel, is used for the values of innermost hashes. By default, this method assumes the key selectors categorizes elements in enum uniquely. If the key selectors generates same keys for two or more elements, ArgumentError is raised. This behavior can be customized by :seed option and the block.

a = [{:fruit => "banana", :color => "yellow", :taste => "sweet", :price => 100},
     {:fruit => "melon", :color => "green", :taste => "sweet", :price => 300},
     {:fruit => "grapefruit", :color => "yellow", :taste => "tart", :price => 200}]
p a.tb_unique_categorize(:fruit, :price)
#=> {"banana"=>100, "melon"=>300, "grapefruit"=>200}

p a.tb_unique_categorize(:color, :price)
# ArgumentError

If the block is given, it is used for combining values in a category. The arguments for the block is a seed and the value extracted by vsel. The return value of the block is used as the next seed. :seed option specifies the initial seed. If :seed is not given, the first value for each category is used for the seed.

p a.tb_unique_categorize(:taste, :price) {|s, v| s + v }
#=> {"sweet"=>400, "tart"=>200}

p a.tb_unique_categorize(:color, :price) {|s, v| s + v }
#=> {"yellow"=>300, "green"=>300}



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# File 'lib/tb/enumerable.rb', line 241

def tb_unique_categorize(*args, &update_proc)
  opts = args.last.kind_of?(Hash) ? args.pop.dup : {}
  if update_proc
    opts[:update] = lambda {|ks, s, v| update_proc.call(s, v) }
  else
    seed = Object.new
    opts[:seed] = seed
    opts[:update] = lambda {|ks, s, v|
      if s.equal? seed
        v
      else
        raise ArgumentError, "ambiguous key: #{ks.map {|k| k.inspect }.join(',')}"
      end
    }
  end
  tb_categorize(*(args + [opts]))
end