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$indexOfBytes (aggregation)

Definition

$indexOfBytes

New in version 3.4.

Searches a string for an occurence of a substring and returns the UTF-8 byte index (zero-based) of the first occurence. If the substring is not found, returns -1.

$indexOfBytes has the following operator expression syntax:

{ $indexOfBytes: [ <string expression>, <substring expression>, <start>, <end> ] }
Operand Description
<string expression>

Can be any valid expression as long as it resolves to a string. For more information on expressions, see Expressions.

If the string expression resolves to a value of null or refers to a field that is missing, $indexOfBytes returns null.

If the string expression does not resolve to a string or null nor refers to a missing field, $indexOfBytes returns an error.

<substring expression> Can be any valid expression as long as it resolves to a string. For more information on expressions, see Expressions.
<start> Optional An integral number that specifies the starting index position for the search. Can be any valid expression that resolves to a non-negative integral number.
<end> Optional An integral number that specifies the ending index position for the search. Can be any valid expression that resolves to a non-negative integral number. If you specify a <end> index value, you should also specify a <start> index value; otherwise, $indexOfBytes uses the <end> value as the <start> index value instead of the <end> value.

Behavior

  • If <string expression> is null, $indexOfBytes returns null.
  • If $indexOfBytes is called on a field that doesn’t exist in the document, $indexOfBytes returns null.
  • If <string expression> is not a string and not null, $indexOfBytes returns an error.
  • If <substring expression> is null, $indexOfBytes returns an error.
  • If <start> or <end> is a negative number, $indexOfBytes returns an error.
  • If <start> is a number greater than <end>, $indexOfBytes returns -1.
  • If <start> is a number greater than the byte length of the string, $indexOfBytes returns -1.
  • If <start> or <end> is given a value that is not an integer, $indexOfBytes returns an error.
  • If the <substring expression> is found multiple times within the <string expression>, then $indexOfBytes returns the index of the first <substring expression> found.

Some short examples to highlight different behavior:

Example Results
{ $indexOfBytes: [ "cafeteria", "e" ] } 3
{ $indexOfBytes: [ "cafétéria", "é" ] } 3
{ $indexOfBytes: [ "cafétéria", "e" ] } -1
{ $indexOfBytes: [ "cafétéria", "t" ] } 5
{ $indexOfBytes: [ "foo.bar.fi", ".", 5 ] } 7
{ $indexOfBytes: [ "vanilla", "ll", 0, 2 ] } -1
{ $indexOfBytes: [ "vanilla", "ll", -1 ] } -1
{ $indexOfBytes: [ "vanilla", "ll", 12 ] } -1
{ $indexOfBytes: [ "vanilla", "ll", 5, 2 ] } -1
{ $indexOfBytes: [ "vanilla", "nilla", 3 ] } -1
{ $indexOfBytes: [ null, "foo" ] } null

Examples

Consider an inventory collection with the following documents:

{ "_id" : 1, "item" : "foo" }
{ "_id" : 2, "item" : "fóofoo" }
{ "_id" : 3, "item" : "the foo bar" }
{ "_id" : 4, "item" : "hello world fóo" }
{ "_id" : 5, "item" : null }
{ "_id" : 6, "amount" : 3 }

The following operation uses the $indexOfBytes operator to retrieve the indexes at which the string foo is located in each item:

db.inventory.aggregate(
   [
     {
       $project:
          {
            byteLocation: { $indexOfBytes: [ "$item", "foo" ] },
          }
      }
   ]
)

The operation returns the following results:

{ "_id" : 1, "byteLocation" : "0" }
{ "_id" : 2, "byteLocation" : "4" }
{ "_id" : 3, "byteLocation" : "4" }
{ "_id" : 4, "byteLocation" : "-1" }
{ "_id" : 5, "byteLocation" : null }
{ "_id" : 6, "byteLocation" : null }

See also

$indexOfCP and $indexOfArray