Project a counter of occurrences from document array

Working with Data
,
2

Hello @Georg_Bote, I have this aggregation which outputs the desired result.

db.collection.aggregate([ 
{ 
  $unwind: "$flags" 
}, 
{ 
  $group: { 
      _id: "$flags", 
      count: { $sum: 1 }, 
      regions: { $first: "$regions" }, 
      doc: { $first: { id: "$id", requestcount: "$requestcount", bookingcount: "$bookingcount" } }  
}}, 
{ 
  $group: { 
      _id: null, 
      flags: { $push: { name: "$_id", count: "$count" }}, 
      regions: { $first: "$regions" }, doc: { $first: "$doc" } 
}},
{ 
  $unwind: "$regions" 
},
{ 
  $group: { 
      _id: "$regions", 
      count: { $sum: 1 }, 
      flags: { $first: "$flags" }, 
      doc: { $first: "$doc" } 
}}, 
{ 
  $group: { 
      _id: null, 
      regions: { $push: { _id: "$_id", count: "$count" }}, 
      flags: { $first: "$flags" }, 
      doc: { $first: "$doc" } 
}},
{ 
  $project: { 
      _id: 0, 
      id: "$doc.id", 
      requestcount: "$doc.requestcount", 
      bookingcount: "$doc.bookingcount",  
      regions: 1, 
      flags: 1 
}}
])

Note that it is possible that your aggregation’s $project is not required.

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