Get position of item in rdf type sequence with sparql - sequence

Question

i have a sequence encoded like this in rdf:
_:blanknode <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq>.
_:blanknode <http://www.w3.org/1999/02/22-rdf-syntax-ns#_0> uri:a.
_:blanknode <http://www.w3.org/1999/02/22-rdf-syntax-ns#_1> uri:b.
_:blanknode <http://www.w3.org/1999/02/22-rdf-syntax-ns#_2> uri:c.
now i want to have the position of a given uri within this list.
is there something like:
SELECT ?position
WHERE {
_:blanknode <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq>.
uri:a <http://www.w3.org/1999/02/22-rdf-syntax-ns#_?position> _:blanknode
}
As a workaround i think i could use:
<http://www.w3.org/1999/02/22-rdf-syntax-ns#_0> uri:value "1".
<http://www.w3.org/1999/02/22-rdf-syntax-ns#_1> uri:value "2".
and so on...
with the query:
SELECT ?position
WHERE {
_:blanknode <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq>.
uri:a ?seqUri _:blanknode.
?seqUri uri:value ?position
}
but there has to be a more elegant way

Answer 1

You could do this using a REPLACE function to remove the namespace part of the URI, and then casting the result to an integer, like so:
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX uri: <http://example.org/>
SELECT (xsd:integer(REPLACE(str(?prop),
"http://www.w3.org/1999/02/22-rdf-syntax-ns#_", "")) as ?pos)
WHERE { [] a rdf:Seq;
?prop uri:a .
}
Result:
pos
---
0