kill the nearly duplicate results that came from the 1:n relations in SPARQL

Question

Is possible to concatenate equivalent results in a SPARQL query? For instance, consider the following RDF data and desired result:

knowledge base:

@prefix gr:<http://purl.org/goodrelations/v1#>.

:prod_A gr:color "Red";
        gr:color "Blue".
:prod_B gr:color "Green".

Ideal Result:

| ?prod   | ?color    |
|---------|-----------|
| :prod_A | Red, Blue |
| :prod_B | Green     |

The only way through that I see is to use something like this:

PREFIX gr:<http://purl.org/goodrelations/v1#>

SELECT ?prod ?color
WHERE {
   ?prod gr:color ?color1.
   OPTIONAL {
       ?prod gr:color ?color2.
       FILTER ( ?color1 != ?color2 )
       bind(concat(?color1,",",?color2) as ?color)
   }

but it will work perfectly only if I have exactly 2 matches. Is there a more general and efficient way to do it?

It will be very useful to kill the nearly duplicate results that came from the 1:n relations.

Answer 1

Modified to include comments from below:

You can try:

PREFIX gr: <http://purl.org/goodrelations/v1#>

SELECT ?prod (GROUP_CONCAT(DISTINCT ?color; separator=',') as ?colors)
WHERE {
    ?prod gr:color ?color.
}
GROUP BY ?prod

example can be found here.