My collection containes documents as follow:
*****************************************************************
/* 1 */

{ "_id" : ObjectId("591dae6ae320467808f1e198"), "scenario" : "delc", "datavalue" : [ " _value: ", "A _value: 8", "B _value: 5", "C _value: 2", "D _value:4" ] }

/* 2 */

{ "_id" : ObjectId("591dae83e320467808f1e199"), "scenario" : "delc", "datavalue" : [ " _value: ", "A _value: 4", "B _value: 5", "C _value: 92", "D _value:94" ] }

/* 3 */

{ "_id" : ObjectId("591dae9ae320467808f1e19a"), "scenario" : "delc", "datavalue" : [ " _value: ", "A _value: 2", "C _value: 2", "D _value:4" ] }

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When I want to search for "datavalue grater than A _value: 6" it does not work (returns all the documents) with simple $match $project as follow :
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db.getCollection('test').aggregate([
{$match : {datavalue :

{ $gt : 'A _value: 6'}

}},
{ $project: { scenario: 1,
datavalue: { $filter: { input: "$datavalue", as: "datavalue",
cond: {
$or: [ { $eq: [

{ $substr: [ "$$datavalue", 0, 1 ] }

, "A" ] } ] } } }
} }])
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If I add another $match (the same as the first one) to the pipeline the results are OK, but if I add a condition "searching for documents with datavalue grater than A _value: 6 and datavalue starts with B" it returns all the documents (I attached an image)