Database

[{"material":"silver","type":"beads","shape":"round","_user":"5f9b78bf1130ca88e2e1d"},{"material":"mixed","type":"jewels","shape":"round","_user":"5f9b78bf1130ca88e2e1d"},{"material":"gold","type":"jewels","shape":"other","_user":"5fda2b717112437f9c06"},{"material":"silver","type":"jewels","shape":"other","_user":"5f9b78bf1130ca88e2e1d"},{"material":"mixed","type":"jewels","shape":"other","_user":"5fda2b717112437f9c706"},]

Query

db.collection.aggregate([{$facet:{categorizedByUser:[{$group:{_id:"$_user",count:{$sum:1}}}],categorizedByMaterial:[{$group:{_id:"$material",count:{$sum:1}}}],categorizedByShape:[{$group:{_id:"$shape",count:{$sum:1}}}],categorizedByType:[{$group:{_id:"$type",count:{$sum:1}}}]}}])

Result