MongoDB聚合,计算数组中的每个项并按项分组
在这里,我有一个类似这样的重复项目数组 [ "gg",, “bb”, “dd”, “cc”, "会",, "aa",, “cc”, "gg",, “bb”, “dd”, “cc”, “bb”, “dd”, "会",, "aa",, ] 我愿意回报的是这样的 { ‘gg’:2, “bb”:3, “dd”:3, “抄送”:2, ll:2, "aa":2,, } 可以用MongoDB聚合完成吗???感谢所有帮助使用和作为聚合pipiline的阶段: 查询: 结果:MongoDB聚合,计算数组中的每个项并按项分组,mongodb,aggregation-framework,Mongodb,Aggregation Framework,在这里,我有一个类似这样的重复项目数组 [ "gg",, “bb”, “dd”, “cc”, "会",, "aa",, “cc”, "gg",, “bb”, “dd”, “cc”, “bb”, “dd”, "会",, "aa",, ] 我愿意回报的是这样的 { ‘gg’:2, “bb”:3, “dd”:3, “抄送”:2, ll:2, "aa":2,, } 可以用MongoDB聚合完成吗???感谢所有帮助使用和作为聚合pipiline的阶段: 查询: 结果: db.collection.aggr
db.collection.aggregate([
{
$unwind: "$items"
},
{
$group: {
_id: "$items",
count: {
$sum: 1
}
}
}
])
{
"_id": "ll",
"count": 2
},
{
"_id": "gg",
"count": 2
},
{
"_id": "bb",
"count": 3
},
{
"_id": "cc",
"count": 3
},
{
"_id": "aa",
"count": 2
},
{
"_id": "dd",
"count": 3
}