From: Greg Hauptmann <greg.hauptmann.ruby@...>
Date: 2008-10-28T09:42:39+09:00
Subject: Re: Hash.merge_add! extension - how does this code look?

thanks all for feedback to date - here's my latest take

------------------------------------
  def merge_add!(h)
    raise "Parameter passed in not a hash" if !h.instance_of?(Hash)

    # normalise input hash to contain arrays
    h.each { |key, value| if !value.instance_of?(Array) then h[key] =
[value] end }

    self.merge!(h) do |key, existing, new|
      existing = existing.instance_of?(Array) ? existing : [existing]
      existing + new
    end
  end
------------------------------------
Macintosh-2:myequity greg$ cat spec/lib/hash_extensions_spec.rb
require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')

describe "merge_add!" do
  before(:each) do
    @empty_hash = {}
    @hash_with_number = {100 => 1}
    @hash_with_array = {100 => [1]}
  end

  it "should raise an error if there is no object passed to the method" do
    lambda{ @empty_hash.merge_add!() }.should raise_error(ArgumentError)
  end
  it "should raise an error if the object passed is not a Hash" do
    lambda{@empty_hash.merge_add!(123)}.should
raise_error(RuntimeError, "Parameter passed in not a hash")
  end
  it "should raise an error if the number of items in the hash in not 1" do
    lambda{@empty_hash.merge_add!({101 => 2, 102 => 3})}.should_not raise_error
  end
  it "should create a new Array & wrap new value as an array" do
    @empty_hash.merge_add!( {101 => 2} )
    @empty_hash[101].should eql([2])
  end
  it "should create a new Array & use the array passed as the value" do
    @empty_hash.merge_add!( {101 => [2]} )
    @empty_hash[101].should eql([2])
  end
  it "should migrate existing value to an Array, then add the new
value, if existing value is NOT an array" do
    @hash_with_number.merge_add!( {100 => 2} )
    @hash_with_number[100].should eql([1, 2])
  end
  it "should migrate add the new value to existing, if existing value
IS an array" do
    @hash_with_array.merge_add!( {100 => 2} )
    @hash_with_array[100].should eql([1, 2])
  end

end



On Mon, Oct 27, 2008 at 5:41 PM, Greg Hauptmann
<greg.hauptmann.ruby@gmail.com> wrote:
> I just noticed the code suggested might have a problem when the
> original hash is empty. That is using the ability to pass a block to
> 'merge!" is good, but when the source hash is empty it does not seem
> to trigger use of the code in the block to merge.
>
> -----code----
>  def merge_add!(h)
>    self.merge!(h) do |key, existing, new|
>      new = new.instance_of?(Array) ? new : [new]
>      existing = existing.instance_of?(Array) ? existing : [existing]
>      existing + new
>    end
>  end
> -------------
> ---in console---
> ?> {}.merge_add!({1 => 100})
> => {1=>100}               <<== DID NOT PUT THE '100' IN AN ARRAY!!
>
>>> {1 => 300}.merge_add!({1 => 100})
> => {1=>[300, 100]}
> --------------
>
> regards
> Greg
>
> On Mon, Oct 27, 2008 at 5:21 PM, Stefan Rusterholz <apeiros@gmx.net> wrote:
>>
>> Greg Hauptmann wrote:
>> > thanks for highlighting this!  Is the quickest way to normalise to Array
>> > via
>> > the following?
>> >     hashitem.instance_of?(Array) ? hashitem : [hashitem]
>>
>> If you're building up the hash yourself then I'd use the following
>> idiom:
>> collector = Hash.new { |h,k| h[k] = [] }
>> collector['key1'] << 'value1'
>> collector['key2'] << 'value1'
>> collector['key1'] << 'value2'
>> p collector
>>
>> Simplifies adding to and reading from the hash. But be aware that with
>> the hash having a different default value than nil, you can't use 'if
>> collector[key] then' to test for existence of a key anymore, you have to
>> use has_key?.
>>
>> If you're not building the hash up yourself, then yes, I'd use what you
>> wroten in an each loop and override the existing value.
>>
>> Regards
>> Stefan
>> --
>> Posted via http://www.ruby-forum.com/.
>>
>
>