First of all store numerical values as numbers. Afterwards you can use a simple statement to calculate the average:
db.collection.aggregate([{
"$group": {
"_id": null,
"avg_bvc": { "$avg": "$bvc" }
}
}])
You can simply use more $avg
aggregation operators to get averages for your other numeric fields:
db.collection.aggregate([{
"$group": {
"_id": null,
"avg_bvc": { "$avg": "$bvc" },
"avg_dollar": { "$avg": "$dollar" }
}
}])