[Fluxus] pdata-op "closest"

[gabor papp]

i am playing with particles. i can read the position of the closest 
particle to each particle by using (pdata-op "closest" "p" i), where 'i' 
is the particle index.

i am also trying to read the colour value of the closest pdata, but it 
didn't work. (pdata-op "closest" "c" i) :

ClosestOperator has no operator for types: 
PN6Fluxus10TypedPDataINS_7dColourEEE and f expected vector (size 3) 
value in pdata-set

because "closest" can be used with either a vector or an index, i was 
thinking that maybe if i submit a vector i get back and index that could 
be used to retrieve the colour value, like:
(let* ((v (pdata-op "closest" "p" i))
        (c (pdata-ref "c" (pdata-op "closest" "p" v)))))
      ...)

but it returned a vector in both cases. or wouldn't it make sense to use 
"closest" with any kind of pdata? i suppose other pdata-op's can be used 
with any kinds of pdata as long as their type matches to the operator.

could you suggest a method how i could do this? thanks in advance.

gabor