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$ltrim (aggregation)

$ltrim

New in version 4.0.

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

$ltrim has the following syntax:

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

The $ltrim 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 the beginning of the input.

The argument can be any valid expression that resolves to a string. The $ltrim operator breaks down the string into individual UTF code point to trim from input.

If unspecified, $ltrim removes whitespace characters, including the null character. For the list of whitespace characters, see Whitespace Characters.

Tip
See also:
  • By default, $ltrim removes whitespace characters, including the null character, from the beginning of the input string:

    Example
    Results
    { $ltrim: { input: " \n good bye \t " } }
    "good bye \t "
  • You can override the default characters to trim using the chars field.

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

    Example
    Results
    { $ltrim: { input: " ggggoodbyeeeee", chars: "ge" } }
    " ggggoodbyeeeee"
  • 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, or d from the start of the input string.

    Example
    Results
    { $ltrim: { input: " ggggoodbyeeeee ", chars: " gd" } }
    "oodbyeeeee "

By default, $ltrim removes the following characters:

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

Consider an inventory collection with the following documents:

{ "_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 $ltrim operator to remove leading whitespaces from the description field:

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

The operation returns the following results:

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