Ruby associative array?

Question

After importing data from an R plugin to my ruby script, I have an array that appears to act like a hash. Does anyone know what's going on here?

r_edges.class
#=> Array < Object

r_edges[0]
#=> returns data from index 0 as expected

r_edges['GO:0010035']
# r_edges['GO:0010035']['edges'] also works
#=> returns data at the index that is named 'GO:0010035', see the to_s output below    

r_edges
#=> [  0] [
[0] [
  [ 0] 2,
  [ 1] 3,
  [ 2] 4,
  [ 3] 5,
  [ 4] 6,
  [ 5] 7,
  [ 6] 8,
  [ 7] 9,
 ...... etc.

r_edges.to_s
#=> "[GO:0006260=[edges=[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 28, 29, 31, 32, 33, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 48, 51, 55, 56, 57, 58, 59, 60, 63, 67, 69, 71, 78, 81, 83, 84, 89, 90, 91, 92, 94, 95, 96, 97, 99, 100, 104, 108, 109, 112, 116, 117, 123, 124]], GO:0006271=[edges=[1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 28, 29, 36, 40, 46, 67]], GO:0022616=[edges=[1, 2, .... etc.

I got the data by using the Ruby Rserve gem and interating with an R S4 object like so:

con = con=Rserve::Connection.new
r_edges = con.eval("SOME S4 OBJECT").to_ruby

It is actually helpful for me to get the 'named index' data when I'm looping through the array but I have no idea how to access that value.

Are you using any other libraries or anything? How are you importing the data? Also, what version of Ruby? — Reinstate Monica -- notmaynard
– Reinstate Monica -- notmaynard, Commented Apr 3, 2014 at 22:23
@XiaogeSu, I am well aware. My question is why is my Array acting like a hash. — Josh
– Josh, Commented Apr 3, 2014 at 22:28

Nick Veys · Accepted Answer · 2014-04-03 22:32:36Z

2

It's behaving funny because Ruby is awesome! It lets you shove functionality into an object without subclassing it.

From the Rserve gem's rlist class:

# Returns an Array with module WithNames included
# * Unnamed list: returns an Array
# * Named List: returns a Hash. Every element without explicit name receive
#   as key the number of element, 1-based
#
def to_ruby
  data=to_a
  data.extend WithNames
  data.names=@names
  data
end

Which shoves the WithNames module into the array, which has a couple methods for [] (look around line 121).

answered Apr 3, 2014 at 22:32

Nick Veys

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1 Comment

Josh Over a year ago

ahhhh! I was searching for class Array in the repo to see if they were opening it up but didn't think about extending just the object.

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