Assume events of either type A, B, C or D are being emitted. I want to detect whenever an event of type A is followed by an event of type B. In other words, I want to detect a sequences, for which Esper's EPL provides the -> operator.
However, what I described above is ambiguous, what I want is the following: Whenever a B is detected, I want it to be matched with the most recent A.
I have been playing around with EPL's syntax, but the best I could come up with was that:
select * from pattern [(every a=A) -> b=B]
This, however, matches each B with the oldest A that occured after the last match. Weird...
Help is much appreciated! :P
I use joins a lot for the simple matching. The other option is match-recognize. The join like this.
select * from B unidirectional, A.std:lastevent()
Related
I'm trying to create a new node with label C and relationships from a-->c and b-->c, but if and only if the whole pattern a-->c,b-->c does exist.
a and b already exist (merged before the rest of the query).
The below query is a portion of the query I want to write to accomplish this.
However, it creates a random empty node devoid of properties and labels and attaches the relationship to that node instead. This shouldn't be possible and is certainty not what I want. How do I stop that from happening?
merge (a: A {id: 1})
merge (b: B {id:1})
with *
call {with a, b
match (a)-[:is_required]->(dummy:C), (a)-[:is_required]->(b)
with count(*) as cnt
where cnt = 0
merge (temp: Temporary {id: 12948125})
merge (a)-[:is_required]->(temp)
return temp
}
return *
Thanks
I think there are a couple of problems here:
There are restrictions on how you can use variables introduced with WITH in a sub-query. This article helps to explain them https://neo4j.com/developer/kb/conditional-cypher-execution/
I think you may be expecting the WHERE to introduce conditional flow like IF does in other languages. WHERE is a filter (maybe FILTER would have been a better choice of keyword than WHERE). In this case you are filtering out 'cnt's where they are 0, but then never reference cnt again, so the merge (temp: Temporary {id: 12948125}) and merge (a)-[:is_required]->(temp) always get executed. The trouble is, due to the above restrictions on using variables inside sub-queries, the (a) node you are trying to reference doesn't exist, it's not the one in the outer query. Neo4j then just creates an empty node, with no properties or labels and links it to the :Temporary node - this is completely valid and why you are getting empty nodes.
This query should result in what you intend:
merge (a: A {id: 1})
merge (b: B {id:1})
with *
// Check if a is connected to b or :C (can't use a again otherwise we'd overwrite it)
optional match(x:A {id: 1}) where exists((a)-[:is_required]->(:C)) or exists((a)-[:is_required]->(b))
with *, count(x) as cnt
// use a case to 'fool' foreach into creating the extra :Temporary node required if a is not related to b or :C
foreach ( i in case when cnt = 0 then [1] else [] end |
merge (temp: Temporary {id: 12948125})
merge (a)-[:is_required]->(temp)
)
with *
// Fetch the :Temporary node if it was created
optional match (a)-[:is_required]->(t:Temporary)
return *
There are apoc procedures you could use to perform conditional query execution (they are mentioned in the linked article). You could also play around with looking for a path from (a) and check its length, rather than introduce a new MATCH and the variable x then checking for the existance of related nodes.
If anyone is having the same problem, the answer is that the Neo4j browser is display nonexistent nodes. The query executes fine…
I am trying to find the most optimal way to create conditional filtering of a Database in AnyLogic. The database, looks as follows:
What I am trying to do is adding in AnyLogic Main window 12 check boxes: P1, P2, P3, ..., T5, T6
If the user checks P1, with reference to the above table, A and B need to be displayed.
If the user checks P2, C needs to be displayed
If the user checks P1 and T2, A needs to be discplayed
In summary, it is like filtering in Excel any set of columns by "x" noting that the other cells have a null value.
To start, I used the following code to filter for P1 only (adding the entries to a collection of type String):
collectionDescription.addAll(
selectFrom( data_base ).
where( data_base.P1.eq("x")).
list( data_base.Col1));
Now to filter for P2 as well, the following can be done:
collectionDescription.addAll(
selectFrom( data_base ).
where( data_base.P1.eq("x")).
where( data_base.P2.eq("x")).
list( data_base.Col1));
Following the above logic, as many "where" conditions as needed can be added. However, there are so many possible combinations (e.g. P1/P2, P1/P2/P3, P1/P3, etc. you can imagine the amount of possible combinations).
So, I thought of a potential solution where I would add as many "where" conditions as there are columns, but instead of adding ".eq("x")", I would add ".eq(varP1)". If a checkbox (e.g. P1) is ticked, varP1 would be equal to "x" (varP1 being a variable of type String). But if the box is unticked, ideally varP1 should take a value that means "where anything" so that the condition would not make any impact. I did not manage to find a way to mimic this behavior.
Sorry for the long post, but I wanted to make sure the situation is as clear as possible. So am I on the right track? Any suggestions on how to fix this? Your suggestions would be highly appreciated.
let's say you have a checkbox associated to a variable varP1 to define what you want... then you can do
selectFrom(db_table)
.where(varP1 ? db_table.db_column.eq("x") : db_table.db_column.isNotNull().or(db_table.db_column.isNull()))
.list();
where anything is what i here did as any value which is either null or not null... so if the box is checked then you will find x, otherwise you will find anything
Here is my issue, I'm working on a project of water supply where I have to merge line features representing pipes if they have the same material of construction and if they are touching each other. The merge is done two by two what it means that some features will be duplicated in some cases like described in the figure below :
this shows exactly my issue. After the merge I will get three records but what I want is just one record which encompasses the whole pipes that fill the conditions put in the where clause :
Here is the query that helps me do the merge :
drop table if exists touches_material;
create table touches_material as
select distinct a.*,
st_Union(a.geom,b.geom) as fusion from pipe a, pipe b
where a.id < b.id and a.material = b.material and
st_touches(a.geom,b.geom)
group by a.id,a.geom,b.geom
the following picture picture shows the expected result on a test data, it's realized via QGIS GIS software :
but this is what I' getting with my query :
if you have any idea about how to achieve the aim that I invoked, I would be very thankful to get an answer from you. Best regards.
New to Esper and EPL in general, i have two use cases which are basically the opposites of oneanother. First I need to catch all unique events in a timewindow, using firstunique(*parameters*).win:time(*time*).
Now what I need to do is the exact opposite, basically catch all events that arrive in that window and that are NOT thrown by that statement, basically all the duplicates.
How can I achieve this ? Thanks !
You could use a subquery and "not exists". For example:
select * from Event e1 where not exists (select * from Event#firstunique(*parameters*)#time(*time*) e2 where e1.parameters = e2.parameters)
I've actually found a solution, it involves using unique id's for incoming events on top of comparing their parameters.
The query looks something like this :
select * from Event a where exists (select * from Event.std:firstUnique(*parameters*).win:time(*time*) b where a.eventId <> b.eventId)
This solves the problem I had where the exists method would return every event (duplicates and unique events) because the window in the subquery would be filled first.
I'd like to pair two sequences D and A with Reactive Extensions in .NET. The resulting sequence R should pair D and A in a way that whenever new data appears on D, it is paired with the latest value from A as visualized in the following diagram:
D-1--2---3---4---
A---a------b-----
R----2---3---4---
a a b
CombineLatest or Zip does not exactly what I want. Any ideas on how this can be achieved?
Thanks!
You want Observable.MostRecent:
var R = A.Publish(_A => D.SkipUntil(_A).Zip(_A.MostRecent(default(char)), Tuple.Create));
Replace char with whatever the element type of your A observable.
Conceptually, the query above is the same as the following query.
var R = D.SkipUntil(A).Zip(A.MostRecent(default(char)), Tuple.Create));
The problem with this query is that subscribing to R subscribes to A twice. This is undesirable behavior. In the first (better) query above, Publish is used to avoid subscribing to A twice. It takes a mock of A, called _A, that you can subscribe to many times in the lambda passed to Publish, while only subscribing to the real observable A once.