# Path length function?
**URL:** https://community.stardog.com/t/path-length-function/3237
**Category:** Support
**Created:** [September 2, 2021, 5:50pm UTC](https://community.stardog.com/t/path-length-function/3237 "2021-09-02T17:50:25Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@lapidus](https://community.stardog.com/u/lapidus)
#### Post date: [September 2, 2021, 5:50pm UTC](https://community.stardog.com/t/path-length-function/3237/1 "2021-09-02T17:50:25Z")
First of all ... it's amazing to see that Stardog always has a helpful article whatever one googles for ...
I googled "using path queries in subqueries" and landed on "Path queries as subqueries": [Stored Query Service](https://www.stardog.com/labs/blog/stored-query-service/)
Follow-up question ...
It says at the bottom of that post:
> "We added one obvious function — `length` — which simply returns the length of a path. One can use it to get the average path length"
Where do I find this function? 😅
I am trying to get an end result like:
startClass, someSuperClass, length (distance)
a, b, 1
a, c, 2
a, d, 3
a, e, 4
Thank you!
---
### Author:  [@pavel](https://community.stardog.com/u/pavel)
#### Post date: [September 2, 2021, 5:59pm UTC](https://community.stardog.com/t/path-length-function/3237/2 "2021-09-02T17:59:00Z")
Hi Daniel,
Thanks for the kind word, appreciate it!
There's one example at [Stored Query Service | Stardog Documentation Latest](https://docs.stardog.com/query-stardog/stored-query-service#path-subqueries:)
```auto
prefix sqs:
prefix stardog:
SELECT ?start (avg(stardog:length(?path)) as ?avg_length) {
SERVICE {
[] sqs:vars ?start, ?path
}
} GROUP BY ?start
```
That groups all paths by the start node and computes their average length.
Best,
Pavel
---
### Author:  [@lapidus](https://community.stardog.com/u/lapidus)
#### Post date: [September 2, 2021, 6:11pm UTC](https://community.stardog.com/t/path-length-function/3237/3 "2021-09-02T18:11:19Z")
Thank you, that solved it!
And again, outstanding documentation and articles. 🌟
---
### Author:  [@lapidus](https://community.stardog.com/u/lapidus)
#### Post date: [September 3, 2021, 10:08am UTC](https://community.stardog.com/t/path-length-function/3237/4 "2021-09-03T10:08:30Z")
@pavel: One more follow up if I may ...
I have two helper functions:
a)
```auto
// Stored Query: GetClassPath
PATHS START ?start END ?end VIA {
?start rdfs:subClassOf ?end .
}
```
b)
```auto
// Stored Query: GetClassDistance
prefix sqs:
SELECT ?start ?end (stardog:length(?path) as ?length) {
service {
[] sqs:vars ?path ; sqs:var:start ?start ; sqs:var:end ?end .
}
}
```
... and a final query that makes use of the above:
```auto
SELECT ?start ?classSubject ?depth {
service {
[] sqs:vars ?path ; sqs:var:start ?start ; sqs:var:end ?classSubject ; sqs:var:length ?depth .
}
# Which classes do we want to target?
FILTER(?start IN (:country))
}
```
My desired response is:
start, classSubject, depth
:country, :country, 0
:country, :place, 1
:country, :object, 2
(edited)
But I don't get :country as a classSubject unless I do `?start rdfs:subClassOf* ?end .` in the first helper function (note the star).
But if I do that the length function doesn't work. All lengths are set to 1.
So question:
a) Can I include the starting class in this chain with the length calculation intact?
b) If it's not possible, is there a way of adding it by UNION/Values to an outer query that uses this?
Happy to demo on a 5-min video call.
Thanks!
---
### Author:  [@pavel](https://community.stardog.com/u/pavel)
#### Post date: [September 3, 2021, 11:36am UTC](https://community.stardog.com/t/path-length-function/3237/5 "2021-09-03T11:36:57Z")
Hi Daniel,
What's in your data? I just quickly checked on this simplest snippet:
```auto
@prefix : .
:country rdfs:subClassOf :place .
:place rdfs:subClassOf :object .
```
and got the expected result. `:country` cannot be a `classSubject` because it's not a super class of anything. It's not a `classSubject` in your desired response either. Am I missing something?
Cheers,
Pavel
---
### Author:  [@lapidus](https://community.stardog.com/u/lapidus)
#### Post date: [September 3, 2021, 11:55am UTC](https://community.stardog.com/t/path-length-function/3237/6 "2021-09-03T11:55:15Z")
Argh, apologies. Typo! My desired response (or any workaround solution) should include :country together with the other ones:
start, classSubject, depth
:country, :country, 0
:country, :place, 1
:country, :object, 2
The idea is to be able to operate over :country, :place, :object when asking for SHACL shape in the next step (outside this example code).
---
### Author:  [@lapidus](https://community.stardog.com/u/lapidus)
#### Post date: [September 3, 2021, 11:57am UTC](https://community.stardog.com/t/path-length-function/3237/7 "2021-09-03T11:57:21Z")
Complete example:
```auto
prefix sqs:
SELECT ?start ?classSubject ?depth ?property ?datatype ?minCount ?maxCount ?class {
# Is there any SHACL shape with class as target?
# And does that SHACL container have any Property shape objects?
?nodeShape sh:targetClass ?classSubject;
sh:property ?propertyShape .
# What property is the PropertyShape targeting?
?propertyShape sh:path ?property .
# What specific SHACL constraints are defined for that property?
OPTIONAL { ?propertyShape sh:minCount ?minCount . }
OPTIONAL { ?propertyShape sh:maxCount ?maxCount . }
OPTIONAL { ?propertyShape sh:class ?class . }
# Start of subquery – runs first to narrow down classes of relevance for shape inheritance
{
# What are the parent classes?
# And what is the distance from the classSubject
# to the top of the class chain (:meta_root)
SELECT ?start ?classSubject ?depth {
service {
[] sqs:vars ?path ; sqs:var:start ?start ; sqs:var:end ?classSubject ; sqs:var:length ?depth .
}
# Which classes do we want shape for?
FILTER(?start IN (:country))
}
}
# Which properties do we want shape for?
#FILTER(?property in (:p_wikidata_id))
}
```
---
### Author:  [@pavel](https://community.stardog.com/u/pavel)
#### Post date: [September 3, 2021, 12:15pm UTC](https://community.stardog.com/t/path-length-function/3237/8 "2021-09-03T12:15:15Z")
Oh I see. Right, you cannot really force a path query to return paths of zero length.
Here's one workaround, modify your `GetClassDistance` as follows:
```auto
prefix sqs:
SELECT ?start ?end ?length {
{
service {
[] sqs:vars ?path ; sqs:var:start ?start ; sqs:var:end ?end .
}
bind (stardog:length(?path) as ?length)
}
union {
?start a owl:Class
bind(?start as ?end)
bind(0 as ?length)
}
}
```
and make sure each class has a declaration axiom, eg. `:country a owl:Class` (they need to be there anyway according to the OWL spec but this workaround relies on them explicitly).
Cheers,
Pavel
---
### Author:  [@lapidus](https://community.stardog.com/u/lapidus)
#### Post date: [September 3, 2021, 12:19pm UTC](https://community.stardog.com/t/path-length-function/3237/9 "2021-09-03T12:19:55Z")
That worked wonders!
Biggest thanks and have a nice weekend!
---
### Author:  [@system](https://community.stardog.com/u/system)
#### Post date: [September 17, 2021, 12:20pm UTC](https://community.stardog.com/t/path-length-function/3237/10 "2021-09-17T12:20:09Z")
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