Grouping similar attributes

[Dominic Son]

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

 

[Brian Candler]

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?

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

 

[James Edward Gray II]

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

Here's one idea:

Person = Struct.newname, :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">]=> {"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 Gray II

 

[Dominic Son]

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.

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

 

[Dominic Son]

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