How to do pivoting on MongoDB? - database

Question

I have this 'Sales' collection and a sample of it looks like this:
[
{cusID: 'a412q39x',
cusCountry: 'MEX',
itemPurchased: 'Toy_A'
},
{cusID: 'r760e11s',
cusCountry: 'USA',
itemPurchased: 'Toy_B'
},
{cusID: 'g723f01z',
cusCountry: 'USA',
itemPurchased: 'Toy_C'
},
{cusID: 'h277p01c',
cusCountry: 'CAN',
itemPurchased: 'Toy_B'
}
]
This is the result I am hoping to achieve.
[
{item: 'Toy_A',
USA: 4,
MEX: 2,
CAN: 1,
BRA: 0
},
{item: 'Toy_B',
USA: 3,
MEX: 0,
CAN: 2,
BRA: 1
}
]
I tried:
{
$group:{_id:{toy:'$itemPurchased', country: $cusCountry'},'cnt':{'$sum': 1}}
}
The result was not what I wanted.
[
{
_id.toy: 'Toy_A',
_id.country: 'BRA',
cnt: 43
},
{
_id.toy: 'Toy_A',
_id.country: 'USA',
cnt: 102
},
{
_id.toy: 'Toy_A',
_id.country: 'JPN',
cnt: 72
},
{
_id.toy: 'Toy_B',
_id.country: 'CAN',
cnt: 32
}
]
I have also experimented with $facet but to no avail. Mongo gurus, please enlighten. Thanks in advance.

Answer 1

Try as below:
db.collection.aggregate([
{
$group: { _id: '$itemPurchased' , items: { $push: { "country" : "$cusCountry", "count": { $sum :1} } } }
},
{
"$project": {
"countryCounts": {
"$arrayToObject": {
"$map": {
"input": "$items",
"as": "item",
"in": {
"k": "$$item.country",
"v": "$$item.count",
}
}
}
}
}
},
{ $replaceRoot: { newRoot: { "$mergeObjects":[ "$countryCounts" , { "item":"$_id"} ] } } }
])
You will get the result like below:
{
"USA" : 1,
"item" : "Toy_C"
},
/* 2 */
{
"USA" : 1,
"CAN" : 1,
"item" : "Toy_B"
},
/* 3 */
{
"MEX" : 1,
"item" : "Toy_A"
}