$in (aggregation)
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Definition
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$in
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New in version 3.4.
Returns a boolean indicating whether a specified value is in an array.
$in
has the following operator expression syntax:Operand Description <expression>
Any valid expression expression. <array expression>
Any valid expression that resolves to an array. Unlike the
$in
query operator, the aggregation$in
operator does not support matching by regular expressions.Example Results { $in: [ 2, [ 1, 2, 3 ] ] }
true
{ $in: [ "abc", [ "xyz", "abc" ] ] }
true
{ $in: [ "xy", [ "xyz", "abc" ] ] }
false
{ $in: [ [ "a" ], [ "a" ] ] }
false
{ $in: [ [ "a" ], [ [ "a" ] ] ] }
true
{ $in: [ /^a/, [ "a" ] ] }
false
{ $in: [ /^a/, [ /^a/ ] ] }
true
Behavior
$in
fails with an error in either of the following cases: if the $in expression is not given exactly two arguments, or if the second argument does not resolve to an array.