$trim (aggregation)

Definition

$trim

Removes whitespace characters, including null, or the specified characters from the beginning and end of a string.

$trim has the following syntax:

{ $trim: { input: <string>,  chars: <string> } }

The $trim takes a document with the following fields:

Field	Description
input	The string to trim. The argument can be any valid expression that resolves to a string. For more information on expressions, see Expressions.
chars	Optional. The character(s) to trim from input. The argument can be any valid expression that resolves to a string. The $trim operator breaks down the string into individual UTF code point to trim from input. If unspecified, $trim removes whitespace characters, including the null character. For the list of whitespace characters, see Whitespace Characters.

Tip

• $ltrim

• $rtrim

Behavior

• By default, $trim removes whitespace characters, including the null character:

  Example	Results
  { $trim: { input: " \n good bye \t " } }	"good bye"

• You can override the default characters to trim using the chars field.

  For example, the following trims any g and e from the start and end of the input. Since the input starts with a whitespace, neither character can be trimmed from the start of the string.

  Example	Results
  { $trim: { input: " ggggoodbyeeeee", chars: "ge" } }	" ggggoodby"

• If overriding the default characters to trim, you can explicitly include the whitespace character(s) to trim in the chars field.

  For example, the following trims any space, g, e from the start and end of the input.

  Example	Results
  { $trim: { input: " ggggoodbyeeeee", chars: " ge" } }	"oodby"

Example

Consider an inventory collection with the following documents:

db.inventory.insertMany( [
   { _id: 1, item: "ABC1", quarter: "13Q1", description: " product 1" },
   { _id: 2, item: "ABC2", quarter: "13Q4", description: "product 2 \n The product is in stock.  \n\n  " },
   { _id: 3, item: "XYZ1", quarter: "14Q2", description: null }
] )

The following operation uses the $trim operator to remove leading and trailing whitespaces from the description field:

db.inventory.aggregate([
   { $project: { item: 1, description: { $trim: { input: "$description" } } } }
])

The operation returns the following results:

{ _id: 1, item: "ABC1", description: "product 1" }
{ _id: 3, item: "XYZ1", description: null }
{ _id: 2, item: "ABC2", description: "product 2 \n The product is in stock." }