In MongoDB, the $split aggregation pipeline operator divides a string into an array of substrings based on a delimiter.

The delimiter is removed from the string, and the substrings are added as elements to the array.

To use $split, you specify the string and the delimiter.

If the delimiter isn’t found in the string, the original string is returned as the only item in the array.

Example 1

Suppose we have a collection called test with the following document:

{ "_id" : 1, "data" : "March-18-2020" }

We can use $split to split the data field at the hyphen.

db.test.aggregate(
   [
     { $match: { _id: 1 } },
     {
       $project:
          {
            _id: 0,
            result: { $split: [ "$data", "-" ] }
          }
     }
   ]
)

Result:

{ "result" : [ "March", "18", "2020" ] }

Example 2

Suppose we have the following document:

{ "_id" : 2, "data" : "Sydney, Australia, NSW 2000" }

We can use $split to separate the data field based on the comma and space:

db.test.aggregate(
   [
     { $match: { _id: 2 } },
     {
       $project:
          {
            _id: 0,
            result: { $split: [ "$data", ", " ] }
          }
     }
   ]
)

Result:

{ "result" : [ "Sydney", "Australia", "NSW 2000" ] }

Example 3

Here’s one more example. This time we’re going to split the string based on the space in between each word.

Sample document:

{ "_id" : 3, "data" : "Homer Jay Einstein" }

Let’s split it up:

db.test.aggregate(
   [
     { $match: { _id: 3 } },
     {
       $project:
          {
            _id: 0,
            result: { $split: [ "$data", " " ] }
          }
     }
   ]
)

Result:

{ "result" : [ "Homer", "Jay", "Einstein" ] }

Wrong Data Type

The two arguments must be strings. Providing the wrong data type results in an error.

Example:

db.test.aggregate(
   [
     { $match: { _id: 1 } },
     {
       $project:
          {
            _id: 0,
            result: { $split: [ "$data", 18 ] }
          }
     }
   ]
)

Result:

Error: command failed: {
	"ok" : 0,
	"errmsg" : "$split requires an expression that evaluates to a string as a second argument, found: double",
	"code" : 40086,
	"codeName" : "Location40086"
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:18:14
_assertCommandWorked@src/mongo/shell/assert.js:639:17
assert.commandWorked@src/mongo/shell/assert.js:729:16
DB.prototype._runAggregate@src/mongo/shell/db.js:266:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1058:12
@(shell):1:1

As the error message states, $split requires an expression that evaluates to a string as a second argument, found: double.