How to limit string field by words not characters in Aggregation?

My Documents looks like this:

{
   "_id" : ObjectId("5e41877df4cebbeaebec5146"),
   "Paragraph" : "My Name is John Smith.I am learning MongoDB database"
}
{
   "_id" : ObjectId("5e4187d7f4cebbeaebec5147"),
   "Paragraph" : "David Miller is a good student and learning Spring and Hibernate Framework."
}

I want to limit Paragraph field text to 5 words like this:

{
   "_id" : ObjectId("5e41877df4cebbeaebec5146"),
   "Paragraph" : "My Name is John Smith."
}
{
   "_id" : ObjectId("5e4187d7f4cebbeaebec5147"),
   "Paragraph" : "David Miller is a good"
}

>Solution :

One option is:

db.collection.aggregate([
  db.collection.aggregate([
  {
    $set: {
      Paragraph: {
        $reduce: {
          input: {
            $slice: [
              {
                $split: [
                  "$Paragraph",
                  " "
                ]
              },
              5
            ]
          },
          initialValue: "",
          in: {
            $concat: [
              "$$value",
              {
                $concat: [
                  "$$this",
                  " "
                ]
              }
            ]
          }
        }
      }
    }
  },
  {
    $set: {
      Paragraph: {
        $substr: [
          "$Paragraph",
          0,
          {
            $subtract: [
              {
                "$strLenCP": "$Paragraph"
              },
              1
            ]
          }
        ]
      },
      
    }
  }
])

See how it works on the playground example