$trim (aggregation)¶

On this page

Definition
Behavior
Example

Definition¶

$trim¶

New in version 4.0.

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.

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"

Whitespace Characters¶

By default, $trim removes the following whitespaces, including the null character:

Unicode	Escape sequence	Description
U+0000	‘0’	Null character
U+0020	‘ ‘	Space
U+0009	‘t’	Horizontal tab
U+000A	‘n’	Line feed/new line
U+000B	‘v’	Vertical tab
U+000C	‘f’	Form feed
U+000D	‘r’	Carriage return
U+00A0		Non-breaking space
U+1680		Ogham space mark
U+2000		En quad
U+2001		Em quad
U+2002		En space
U+2003		Em space
U+2004		Three-per-em space
U+2005		Four-per-em space
U+2006		Six-per-em space
U+2007		Figure space
U+2008		Punctuation space
U+2009		Thin space
U+200A		Hair space

Example¶

Consider an inventory collection with the following documents:

copy

{ "_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:

copy

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

The operation returns the following results:

copy

{ "_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." }

← $toUpper (aggregation) $trunc (aggregation) →