Array Aggregation Operators¶

注解

For details on specific operator, including syntax and examples, click on the specific operator to go to its reference page.

Name	Description
`$arrayElemAt`	Returns the element at the specified array index.
`$concatArrays`	Concatenates arrays to return the concatenated array.
`$filter`	Selects a subset of the array to return an array with only the elements that match the filter condition.
`$indexOfArray`	Searches an array for an occurence of a specified value and returns the array index of the first occurence. If the substring is not found, returns `-1`.
`$isArray`	Determines if the operand is an array. Returns a boolean.
`$range`	Outputs an array containing a sequence of integers according to user-defined inputs.
`$reverseArray`	Returns an array with the elements in reverse order.
`$reduce`	Applies an expression to each element in an array and combines them into a single value.
`$size`	Returns the number of elements in the array. Accepts a single expression as argument.
`$slice`	Returns a subset of an array.
`$zip`	Merge two lists together.
`$in`	Returns a boolean indicating whether a specified value is in an array.