Grouping similar attributes

Ruby
1

How would one group attributes which came from an array/db?

For example in my DB:

| NAME | ETHNIC |

| Dominic | Asian |

| John | Asian |

| Rick | Spanish |

I’d like it to group by Ethnicity:

Asian

  • Dominic
  • John

Spanish

  • Rich

Is there some ruby thing that makes this convenient?

Thanks a whole bunch.

Dominic

2

On Fri, Feb 09, 2007 at 12:12:42AM +0900, Dominic S. wrote:

  • Rich

Is there some ruby thing that makes this convenient?

d = {
‘Dominic’ => ‘Asian’,
‘John’ => ‘Asian’,
‘Rick’ => ‘Spanish’,
}

Unfortunately this doesn’t quite do what you want:

i = d.invert
puts i.inspect

So:

j = Hash.new { [] }
d.each { |k,v| j[v] <<= k }
puts j.inspect

3

On Feb 8, 2007, at 9:12 AM, Dominic S. wrote:

  • Rich
    Here’s one idea:

Person = Struct.new(:name, :ethnic)
=> Person

people = [Person.new(“Dominic”, “Asian”), Person.new(“John”,
“Asian”), Person.new("Rick, “Spanish”)]
^C

people = [Person.new(“Dominic”, “Asian”), Person.new(“John”,
“Asian”), Person.new(“Rick”, “Spanish”)]
=> [#<struct Person name=“Dominic”, ethnic=“Asian”>, #<struct Person
name=“John”, ethnic=“Asian”>, #<struct Person name=“Rick”,
ethnic=“Spanish”>]

by_ethnic = Hash.new
=> {}

people.each do |person|
?> (by_ethnic[person.ethnic] ||= Array.new) << person

end
=> [#<struct Person name=“Dominic”, ethnic=“Asian”>, #<struct Person
name=“John”, ethnic=“Asian”>, #<struct Person name=“Rick”,
ethnic=“Spanish”>]

by_ethnic
=> {“Asian”=>[#<struct Person name=“Dominic”, ethnic=“Asian”>,
#<struct Person name=“John”, ethnic=“Asian”>], “Spanish”=>[#<struct
Person name=“Rick”, ethnic=“Spanish”>]}

Hope that helps.

James Edward G. II

4

This can help you too…

def ethnic_group(e, n)

 if @eg.nil?
    @eg = {}
 end

 if @eg[e].nil?
    @eg[e] = []
 end

 @eg[e] << n
 return @eg

end

@eg = nil

ethnic_group(‘asian’, ‘domnic’)
ethnic_group(‘asian’, ‘john’)
ethnic_group(‘spanish’, ‘rich’)

p @eg

5

Looks good. that would’ve been nifty if there was a function to automate
this…for now looks like we’re rolling our own… i’ll be playing with
these suggestions. thanks.

SunRaySon wrote:

This can help you too…

def ethnic_group(e, n)

 if @eg.nil?
    @eg = {}
 end

 if @eg[e].nil?
    @eg[e] = []
 end

 @eg[e] << n
 return @eg

end

@eg = nil

ethnic_group(‘asian’, ‘domnic’)
ethnic_group(‘asian’, ‘john’)
ethnic_group(‘spanish’, ‘rich’)

p @eg

6

btw, I’m going with Brian’s technique as it’s the least to type : P and
it works beautifully… thanks again.

Dominic S. wrote:

Looks good. that would’ve been nifty if there was a function to automate
this…for now looks like we’re rolling our own… i’ll be playing with