I am still learning about python and I face some trouble extracting data from a dict. I need to create a loop which check each values and extract the keys. So for this code I need to find the nice students. I am stuck at line 3 #blank.
How do i go about this?
Thanks in advance
class = {"James":"naughty", "Lisa":"nice", "Bryan":"nice"}
for student in class:
if #blank:
print("Hello, "+student+" students!")
else:
print("odd")
Uses dictionary methods "keys(), values(), items()":
def get_students_by_criteria(student_class, criteria):
students = []
for candidate, value in student_class.items():
if value == criteria:
students.append(candidate)
return students
my_class = {"James":"naughty", "Lisa":"nice", "Bryan":"nice"}
print(get_students_by_criteria(my_class, "nice"))
Warning to the word "class" it is a keyword reserved for python programming oriented object
I am working on julia with the Metagraphs.jl library.
In order to conduct an optimization problem, I would like to get the set/list of edges in the graph that point to a special set of vertices having 2 particular properties in common.
My first guess was to first get the set/list of vertices. But I am facing a first issue which is that the filter_vertices function doesn't seem to accept to apply a filter on more than one property.
Here is below an example of what I would like to do:
g = DiGraph(5)
mg = MetaDiGraph(g, 1.0)
add_vertex!(mg)
add_edge!(mg,1,2)
add_edge!(mg,1,3)
add_edge!(mg,1,4)
add_edge!(mg,2,5)
add_edge!(mg,3,5)
add_edge!(mg,5,6)
add_edge!(mg,4,6)
set_props!(mg,3,Dict(:prop1=>1,:prop2=>2))
set_props!(mg,1,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,2,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,4,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,5,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,6,Dict(:prop1=>0,:prop2=>0))
col=collect(filter_vertices(mg,:prop1,1,:prop2,2))
And I want col to find vertex 3 and no others.
But the filter_vertices would only admit one property at a time and then it makes it more costly to do a loop with 2 filters and then try to compare in order to sort a list with the vertices that have both properties.
Considering the size of my graph I would like to avoid defining this set with multiple and costly loops. Would any one of you have an idea of how to solve this issue in an easy and soft way?
I ended up making this to answer my own question:
fil3=Array{Int64,1}()
fil1=filter_vertices(mg,:prop1,1)
for f in fil1
if get_prop(mg,f,:prop2)==2
push!(fil3,f)
end
end
println(fil3)
But tell me if you get anything more interesting
Thanks for your help!
Please provide a minimal working example in a way we can simply copy and paste, and start right away. Please also indicate where the problem occurs in the code. Below is an example for your scenario:
Pkg.add("MetaGraphs")
using LightGraphs, MetaGraphs
g = DiGraph(5)
mg = MetaDiGraph(g, 1.0)
add_vertex!(mg)
add_edge!(mg,1,2)
add_edge!(mg,1,3)
add_edge!(mg,1,4)
add_edge!(mg,2,5)
add_edge!(mg,3,5)
add_edge!(mg,5,6)
add_edge!(mg,4,6)
set_props!(mg,3,Dict(:prop1=>1,:prop2=>2))
set_props!(mg,1,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,2,Dict(:prop1=>1,:prop2=>0))
set_props!(mg,4,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,5,Dict(:prop1=>0,:prop2=>2))
set_props!(mg,6,Dict(:prop1=>0,:prop2=>0))
function my_vertex_filter(g::AbstractMetaGraph, v::Integer, prop1, prop2)
return has_prop(g, v, :prop1) && get_prop(g, v, :prop1) == prop1 &&
has_prop(g, v, :prop2) && get_prop(g, v, :prop2) == prop2
end
prop1 = 1
prop2 = 2
col = collect(filter_vertices(mg, (g,v)->my_vertex_filter(g,v,prop1,prop2)))
# returns Int[3]
Please check ?filter_vertices --- it gives you a hint on what/how to write to define your custom filter.
EDIT. For filtering the edges, you can have a look at ?filter_edges to see what you need to achieve the edge filtering. Append the below code excerpt to the solution above to get your results:
function my_edge_filter(g, e, prop1, prop2)
v = dst(e) # get the edge's destination vertex
return my_vertex_filter(g, v, prop1, prop2)
end
myedges = collect(filter_edges(mg, (g,e)->my_edge_filter(g,e,prop1,prop2)))
# returns [Edge 1 => 3]
I found this solution:
function filter_function1(g,prop1,prop2)
fil1=filter_vertices(g,:prop1,prop1)
fil2=filter_vertices(g,:prop2,prop2)
filter=intersect(fil1,fil2)
return filter
end
This seems to work and is quite easy to implement.
Just I don't know if the filter_vertices function is taking a lot of computational power.
Otherwise a simple loop like this seems to also work:
function filter_function2(g,prop1,prop2)
filter=Set{Int64}()
fil1=filter_vertices(g,:prop1,prop1)
for f in fil1
if get_prop(g,f,:prop2)==prop2
push!(filter,f)
end
end
return filter
end
I am open to any other answers if you have some more elegant ones.
I'm trying to copy a vertex node and retain it's relationships in ArangoDB. I'm getting a "access after data-modification" error (1579). It doesn't like it when I iterate over the source node's edges and insert an edge copy within the loop. This makes sense but I'm struggling to figure out how to do what I'm wanting within a single transaction.
var query = arangojs.aqlQuery`
let tmpNode = (FOR v IN vertices FILTER v._id == ${nodeId} RETURN v)[0]
let nodeCopy = UNSET(tmpNode, '_id', '_key', '_rev')
let nodeCopyId = (INSERT nodeCopy IN 'vertices' RETURN NEW._id)[0]
FOR e IN GRAPH_EDGES('g', ${nodeId}, {'includeData': true, 'maxDepth': 1})
let tmpEdge = UNSET(e, '_id', '_key', '_rev')
let edgeCopy = MERGE(tmpEdge, {'_from': nodeCopyId})
INSERT edgeCopy IN 'edges'
`;
This quesion is somewhat similar to 'In AQL how to re-parent a vertex' - so let me explain this in a similar way.
One should use the ArangoDB 2.8 pattern matching traversals to solve this.
We will copy Alice to become Sally with similar relations:
let alice=DOCUMENT("persons/alice")
let newSally=UNSET(MERGE(alice, {_key: "sally", name: "Sally"}), '_id')
let r=(for v,e in 1..1 ANY alice GRAPH "knows_graph"
LET me = UNSET(e, "_id", "_key", "_rev")
LET newEdge = (me._to == "persons/alice") ?
MERGE(me, {_to: "persons/sally"}) :
MERGE(me, {_from: "persons/sally"})
INSERT newEdge IN knows RETURN newEdge)
INSERT newSally IN persons RETURN newSally
We therefore first load Alice. We UNSET the properties ArangoDB should set on its own. We change the properties that have to be uniq to be uniq for Alice so we have a Sally afterwards.
Then we open a subquery to traverse ANY first level relations of Alice. In this subequery we want to copy the edges - e. We need to UNSET once more the document attributes that have to be autogenerated by ArangoDB. We need to find out which side of _from and _to pointed to Alice and relocate it to Sally.
The final insert of Sally has to be outside of the subquery, else this statement will attempt to insert one Sally per edge we traverse. We can't insert Saly in front of the query as you already found out - no subsequent fetches are allowed after the insert.
We have a smaller example twitter database:
user -[TWEETED]-> tweet -[MENTIONED]-> user2
and I would like to find out how to write a query in Gremlin, that shows who were the users who mentioned each other. I have already read the docs but I don't know how to do it.
Given this sample data that assume marko and stephen mention each other and marko and daniel mention each other:
g = new TinkerGraph()
vMarko = g.addVertex("marko", [type:"user"])
vStephen = g.addVertex("stephen", [type:"user"])
vDaniel = g.addVertex("daniel", [type:"user"])
vTweetm1s = g.addVertex("m1s", [type:"tweet"])
vTweetm2d = g.addVertex("m2d", [type:"tweet"])
vTweets1m = g.addVertex("s1m", [type:"tweet"])
vTweetd1m = g.addVertex("d1m", [type:"tweet"])
vMarko.addEdge("tweeted",vTweetm1s)
vMarko.addEdge("tweeted",vTweetm2d)
vStephen.addEdge("tweeted",vTweets1m)
vDaniel.addEdge("tweeted",vTweetd1m)
vTweetm1s.addEdge("mentioned", vStephen)
vTweetm2d.addEdge("mentioned", vDaniel)
vTweets1m.addEdge("mentioned", vMarko)
vTweetd1m.addEdge("mentioned", vMarko)
you could handle it with the following:
gremlin> g.V.has("type","user").as('s')
.out("tweeted").out("mentioned").as('m').out("tweeted")
.out("mentioned").as('e').select.filter{it[0]==it[2]}
==>[s:v[daniel], m:v[marko], e:v[daniel]]
==>[s:v[stephen], m:v[marko], e:v[stephen]]
==>[s:v[marko], m:v[stephen], e:v[marko]]
==>[s:v[marko], m:v[daniel], e:v[marko]]
This approach uses select to extract the data from the labelled steps then a final filter to find those where "s" (vertex in the first position) is equal to the "e" (vertex in the final position). This of course means that there is cycle pattern detected where the one user mentioned another and the other mentioned that person back at some point.
If you follow that much then we can clean up the result a little bit so as to get the unique set of pairs:
gremlin> g.V.has("type","user").as('s')
.out("tweeted").out("mentioned").as('m')
.out("tweeted").out("mentioned").as('e')
.select.filter{it[0]==it[2]}
.transform{[it[0].id,it[1].id] as Set}.toList() as Set
==>[daniel, marko]
==>[stephen, marko]
By adding a transform to the previous code, we can convert the result to "id" (the user's name in this case) and flip everything to Set so as to get unique pairs of results.
First off, yes this is homework - please suggest where I am going wrong,but please do not do my homework for me.
I am learning XQuery, and one of my tasks is to take a list of song ID's for a performance and determine the total duration of the performance. Given the snippits below, can anyone point me to where I can determine how to cross reference the songID from the performance to the duration of the song?
I've listed my attempts at the end of the question.
my current XQuery code looks like:
let $songIDs := doc("C:/Users/rob/Downloads/A4_FLOWR.xml")
//SongSet/Song
for $performance in doc("C:/Users/rob/Downloads/A4_FLOWR.xml")
//ContestantSet/Contestant/Performance
return if($performance/SongRef[. =$songIDs/#SongID])
then <performanceDuration>{
data($performance/SongRef)
}</performanceDuration>
else ()
Which outputs:
<performanceDuration>S005 S003 S004</performanceDuration>
<performanceDuration>S001 S007 S002</performanceDuration>
<performanceDuration>S008 S009 S006</performanceDuration>
<performanceDuration>S002 S004 S007</performanceDuration>
Each S00x is the ID of a song, which us found in the referenced xml document (partial document):
<SongSet>
<Song SongID="S001">
<Title>Bah Bah Black Sheep</Title>
<Composer>Mother Goose</Composer>
<Duration>2.99</Duration>
</Song>
<Song SongID="S005">
<Title>Thank You Baby</Title>
<Composer>Shania Twain</Composer>
<Duration>3.02</Duration>
</Song>
</SongSet>
The performance section looks like:
<Contestant Name="Fletcher Gee" Hometown="Toronto">
<Repertoire>
<SongRef>S001</SongRef>
<SongRef>S002</SongRef>
<SongRef>S007</SongRef>
<SongRef>S010</SongRef>
</Repertoire>
<Performance>
<SongRef>S001</SongRef>
<SongRef>S007</SongRef>
<SongRef>S002</SongRef>
</Performance>
</Contestant>
My Attempts
I thought I would use nested loops, but that fails:
let $songs := doc("C:/Users/rob/Downloads/A4_FLOWR.xml")
//SongSet/Song
for $performance in doc("C:/Users/rob/Downloads/A4_FLOWR.xml")
//ContestantSet/Contestant/Performance
return if($performance/SongRef[. =$songs/#SongID])
for $song in $songIDs
(: gives an error in BaseX about incomplete if :)
then <performanceDuration>{
data($performance/SongRef)
}</performanceDuration>
else ()
--Edit--
I've fixed the inner loop, however I am getting all the songs durations, not just the ones that match id's. I have a feeling that this is due to variable scope, but I'm not sure:
let $songs := doc("C:/Users/rob/Downloads/A4_FLOWR.xml")//SongSet/Song
for $performance in doc("C:/Users/rob/Downloads/A4_FLOWR.xml")//ContestantSet/Contestant/Performance
return if($performance/SongRef[. =$songs/#SongID])
then <performanceDuration>{
for $song in $songs
return if($performance/SongRef[. =$songs/#SongID])
then
sum($song/Duration)
else ()
}</performanceDuration>
else ()
}
Output:
<performanceDuration>2.99 1.15 3.15 2.2 3.02 2.25 3.45 1.29 2.33 3.1</performanceDuration>
Your immediate problem is syntactic: you've inserted your inner loop between the condition and the keyword 'then' in a conditional. Fix that first:
return if ($performance/SongRef = $songs/#SongID) then
<performanceDuration>{
(: put your inner loop HERE :)
}</performanceDuration>
else ()
Now think yourself into the situation of the query evaluator inside the performanceDuration element. You have the variable $performance, you can find all the song references using $performance/SongRef, and for each song reference in the performance element, you can find the corresponding song element by matching the SongRef value with $songs/#SongID.
My next step at this point would be to ask myself:
For a given song reference, how do I find the song element for that song, and then the duration for that song?
Is there a way to get the sum of some set of durations? Is there, for example, a sum() function? (I'm pretty sure there is, but at this point I always pull up the Functions and Operators spec and look it up to be sure of the signature.)
What type does the duration info have? I'd expect it to be minutes and seconds, and I'd be worrying about duration arithmetic, but your sample makes it look like decimals, which will be easy.