Hi have a MongoDB collection matchedpairs with a data structure as follows:
each document defines a pairwise connection with each other, i.e 1 is in union with 2 and 2 is in union with 10 etc. There are a large number of relationships defined.
{
x:1,
y:2
},
{
x:2,
y:10
},
{
x:9,
y:10
},
{
x:8,
y:4
}
I would like to query the documents and retrieve the unique disjoint sets for the pairs, i.e. return a result like this
{
set:[1,2,9,10]
},
{
set:[8,4]
}
I am familiar with the aggregation framework, but cannot see how to create the correct accumulator in the $group stage to create the disjoint sets. The attempt below simply gives just one grouping of similar pairs. As I see it I would have to create a whole string of $group stages (depending upon my set of data) to get the result I am looking for. Any clever ideas here?
db.matchedpairs.aggregate([
{
'$group': {
'_id': '$y',
'like': {
'$addToSet': '$x'
},
'from': {
'$addToSet': '$y'
}
}
}, {
'$project': {
'_id': 0,
'set': {
'$setUnion': [
'$like', '$from'
]
}
}
}
]
gives:
{
set:[4,8]
},
{
set:[10,2,9]
},
{
set:[1,2]
}
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