Mongodb aggregate - remove whitespace and letters from name

Question

I have the following group function in my mongodb aggregate:

    {
      $group: {
        _id: "$group.name",
        studentSchoolIDs: {
          $push: "$student_school._id",
        },
      },
    },

This works fine, however before this, i would like to change the group names to remove any spaces or letters. For example "Y 2" would become "2" and "Year 2" would become "2". Is there a way to do that in the aggregate?

Answer 1

Query

• we dont have a regex-replace in mongodb yet, but we have a regex-find, so we can do it using a reduce also

*you can put the reduce on grouping, or you do it after on the _id for example replace "name" with "_id" after the group

To remove letters and spaces

Playmongo

aggregate(
[{"$set": 
   {"name": 
     {"$reduce": 
       {"input": 
         {"$regexFindAll": {"input": "$name", "regex": "[a-zA-Z]+|\\s+"}},
        "initialValue": "$name",
        "in": 
         {"$replaceOne": 
           {"input": "$$value", "find": "$$this.match", "replacement": ""}}}}}}])

To keep only the digits

Playmongo

aggregate(
[{"$set": 
   {"name": 
     {"$reduce": 
       {"input": {"$regexFindAll": {"input": "$name", "regex": "\\d+"}},
        "initialValue": "",
        "in": {"$concat": ["$$value", "$$this.match"]}}}}}])