Mongodb: Converting numeric string to number

Question

How can we convert a numeric string to number in Mongodb?

Actual Problem: Collection: try Two Sample documents stored in try collection:

{
  _id: "1"
  testField: 150
}


{
  _id: "A"
  testField: 140
}

I want to filter out the _id field in the project phase for further processing in group phase. The query below is working fine but I need better solution for it like using type or any other method.

db.try.aggregate([{$match: {"_id":{$in:["1","2","3","4","5","6","7","8","9"]}}}, {$group:{"_id":0, total: {$sum:"$testField"}}}])

This query will give all _id db.try.find({"_id":{$type:2}}). As '_id' will be always string, it is not meaningful query. Can you provide more details please? Furthermore you can follow link docs.mongodb.org/manual/reference/operator/query/type — Vishwas
– Vishwas, Commented Apr 22, 2015 at 10:49
@Vishwas what's the benefit of this query? This will not differentiate between "1" and "A". — Dev
– Dev, Commented Apr 22, 2015 at 10:54
@CodeCore you want to find numeric ids which were saved as string. Right? — Dev
– Dev, Commented Apr 22, 2015 at 11:02
Also, you are using $in for 1-9. Do you have only 9 records(as _id is unique) ? — Dev
– Dev, Commented Apr 22, 2015 at 11:06
@CodeCore solution by Karthik will work for any number of digit. — Dev
– Dev, Commented Apr 22, 2015 at 11:27

karthik manchala · Accepted Answer · 2015-04-22 11:09:10Z

2

You can use regex in this case:

db.try.aggregate([{$match: {"_id":
{$in:[/\d+/]}}}, 
{$group:{"_id":0, total: {$sum:"$testField"}}}])

answered Apr 22, 2015 at 11:09

karthik manchala

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Comments

chridam · Accepted Answer · 2015-04-22 11:24:24Z

An alternative is to use MapReduce where in your map function you can check whether an _id contains a number:

Sample documents:

db.try.insert([
    {
      _id: "1",
      testField: 150
    },
    {
      _id: "2",
      testField: 150
    },
    {
      _id: "A",
      testField: 140
    },
    {
      _id: "B",
      testField: 140
    }
]);

MapReduce:

var map = function(){
    var numeric_id = !isNaN(this._id) ? "numeric" : "non_numeric";
    emit(numeric_id, this.testField); 
};

var reduce = function(key, values) {
    return Array.sum(values);
};

db.try.mapReduce(
    map,
    reduce,
    { out: "try_totals" }
);

Result:

db.try_totals.find()

/* 0 */
{
    "_id" : "non_numeric",
    "value" : 280
}

/* 1 */
{
    "_id" : "numeric",
    "value" : 300
}

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