Mongodb $group需要一个数组,用于_id,但$out-won';我受不了
我需要对数组的出现次数求和。我需要将其输出到一个集合,但当我尝试使用Mongodb $group需要一个数组,用于_id,但$out-won';我受不了,mongodb,aggregation-framework,Mongodb,Aggregation Framework,我需要对数组的出现次数求和。我需要将其输出到一个集合,但当我尝试使用$out关键字时,它失败了,出现了“不能为_id使用数组” 有没有办法将\u id字段的值从group stage投射到一个新键中,并创建一个新的\u id db.djnNews_filtered.aggregate([ {$unwind:"$processed_text.headline_trigrams"}, {$group:{_id:"$processed_text.headline_trigrams","num":{$s
$out
关键字时,它失败了,出现了“不能为_id使用数组”
有没有办法将\u id
字段的值从group stage投射到一个新键中,并创建一个新的\u id
db.djnNews_filtered.aggregate([
{$unwind:"$processed_text.headline_trigrams"},
{$group:{_id:"$processed_text.headline_trigrams","num":{$sum:1}}},
{$sort:{"num":-1}}
])
{ "_id" : [ "Reports", "First", "Quarter" ], "num" : 279 }
{ "_id" : [ "ST", "upside", "prevails" ], "num" : 167 }
{ "_id" : [ "First", "Quarter", "Results" ], "num" : 160 }
{ "_id" : [ "Announces", "First", "Quarter" ], "num" : 155 }
db.djnNews_filtered.aggregate([
{$unwind:"$processed_text.headline_trigrams"},
{$group:{_id:"$processed_text.headline_trigrams","num":{$sum:1}}},
{$sort:{"num":-1}},
{$out:"new_collection"}
])
assert: command failed: {
"errmsg" : "exception: insert for $out failed: { connectionId: 3, err: \"can't use an array for _id\", code: 2, n: 0, ok: 1.0 }",
"code" : 16996,
"ok" : 0
} : aggregate failed
在MongoDB中,不能有一个id为数组的文档 你能简单地
$project
将数组添加到另一个字段吗
db.djnNews_filtered.aggregate([
{$unwind:"$processed_text.headline_trigrams"},
{$group:{_id:"$processed_text.headline_trigrams","num":{$sum:1}}},
{$sort:{"num":-1}},
{$project: {trigram: "$_id", count: "$num"}},
{$out:"new_collection"}
])
另外,我不确定您在将文档插入集合之前对其进行排序的目的是什么。如果这种类型只用于查看数据,然后才决定将其添加到集合中,您可能需要考虑删除该步骤。是的,排序只是为了查看数据。