Count on non existing edges to other node with specific property

[Hoda Moradi]

Hi all,

Pardon my novice question here. I am new in gremlin. I am trying to do a simple count on the non existing edges. I can separately count number students in a university and separately count how many students have math class. I am interested to get the negative count which is how many student in each university does not have a math class and order this count. So my query looks like something like this so far.

 g.V().hasLabel("student").has("university_name","MIT").as("u").groupCount("a").by("university_name").group("b").by("university_name").by(bothE("has").otherV().has("name","math").count()).cap("a","b")

my result looks like this

total number of students are 200 and 50 of them has taken math

[a:[MIT:200],b:[MIT:50]]

I want my results to be

MIT=150

which means 150 students did not taken math class yet. Then I want to order this count for every university.

[Daniel Kuppitz]

Since MIT is part of your query, you don't really need it in your result. Hence, instead of MIT=150, just 150 should be fine.

Also, it doesn't look like you need both() - replace that with out() or in(), depending on your schema.

g.V().has("student","university_name","MIT").

  not(both("has").has("name","math")).

  count()

And if the math class is a vertex uniquely identified by its name, you should do this:

g.V().has("class","name","math").as("c").

  V().has("student","university_name","MIT").

  not(where(both("has").as("c"))).

  count()

It's cheaper to check adjacent vertices by their id, instead of than scanning their properties.

Cheers,

Daniel

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[Hoda Moradi]

Thanks Daniel for your response.

I actually need the MIT because I want to generalize for every university then order by the count. So my query should return something like

MIT=150

UTD=20

....

So how should I change the query to group by the university_name and give me the number of students who do not have the mat class. Also Math class is a vertex.

Thanks again,

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[Daniel Kuppitz]

Then it's:

g.V().hasLabel("student").

  group().

    by("university_name").

    by(__.not(both("has").has("name","math")).count())

Cheers,

Daniel

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[Hoda Moradi]

Thank you so much for your help,

I have a different question as well. I came to know you are one of the committers on the IncrementalBulkloader code. I know it only accepts single value properties, I wanted to ask did it had any edge case or any specific problem that you decided to only accept single values? I need to load lists as property and I wanted to use IncrementalBulkloader. I know I have to implement new BulkloaderVertexProgram. Can you guide me which part of your code should I change and what edge cases I may find?

[Daniel Kuppitz]

I believe it was just because it's unclear how to handle duplicate values in incremental loading. The part that overwrites the current value is right here:

https://github.com/apache/tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/bulkloading/IncrementalBulkLoader.java#L90

I think that's all you need to change to support multi-values.

Cheers,

Daniel

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