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$mod (aggregation)

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$mod

Divides one number by another and returns the remainder.

The $mod expression has the following syntax:

{ $mod: [ <expression1>, <expression2> ] }

The first argument is the dividend, and the second argument is the divisor; i.e. first argument is divided by the second argument.

The arguments can be any valid expression as long as they resolve to numbers. For more information on expressions, see Expressions.

Consider a planning collection with the following documents:

{ "_id" : 1, "project" : "A", "hours" : 80, "tasks" : 7 }
{ "_id" : 2, "project" : "B", "hours" : 40, "tasks" : 4 }

The following aggregation uses the $mod expression to return the remainder of the hours field divided by the tasks field:

db.planning.aggregate(
[
{ $project: { remainder: { $mod: [ "$hours", "$tasks" ] } } }
]
)

The operation returns the following results:

{ "_id" : 1, "remainder" : 3 }
{ "_id" : 2, "remainder" : 0 }

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