group_by: An optional list of attributes over which the grouping should occur.
aggregations: A list of aggregate functions (see below).
processMetaData: Boolean flag set to true if other meta data than Time Interval (e.g. Latency) should be processed.

The following optional boolean parameters control when a new aggregation value is transferred (see below for useful examples):

eval_at_new_element: Outputs an updated aggregation value when a new element gets valid. In the case that more than one element gets valid at the same time (same start timestamp), this operator outputs for each element an output value in the order of arrival. The default value is true.
eval_at_outdating: Outputs an updated aggregation value when one ore more elements gets invalid with the value after the removal of the invalid elements. The default value is true.
eval_before_remove_outdating: Outputs an updated aggregation value before removing the invalid elements instead of after removal. The default value is false.
eval_at_done: Outputs the value at the time the operator gets the done signal. The default value is false.
output_only_changes: Suppresses elements that are equal to the previous outputted element. The default value is false. If you want to use this, make sure the equals-method for every attribute type is implemented.

Aggregation Functions

Function Name Description Parameters Examples

Count

Outputs the number of steam elements.

Name	Description	Default Value	Optional?
`OUTPUT_ATTRIBUTES`	The name for the output attribute.	`count`	True

['FUNCTION' = 'Count']

['FUNCTION' = 'Count', 'OUTPUT_ATTRIBUTES' = 'number_of_elements']

Sum

Outputs the sum of elements.

Name	Description	Default Value	Optional?
INPUT_ATTRIBUTES	The single string or a list of the name(s) of the attribute(s) in the input tuples. By default, all input attributes are used. This could raise an error if attributes are not numeric.	(all attributes)	True
OUTPUT_ATTRIBUTES	A single string or list of output attributes. By default, the string "Sum_" concatenated with the original input attribute name is used.	"Sum_" + intput attribute name	True

['FUNCTION' = 'Sum']

['FUNCTION' = 'Sum', 'INPUT_ATTRIBUTES' = 'value1']

['FUNCTION' = 'Sum', 'INPUT_ATTRIBUTES' = ['value1', 'value2']]

Avg Average value (mean) TODO (similar to Sum)

Min Min value TODO (similar to Sum)

Max Max value TODO (similar to Sum)

First

The first element of a window. See example below.

Name	Description	Default Value	Optional?
`OUTPUT_ATTRIBUTES`	The name for the output attribute.	`first`	True

You should use the following settings:

output_only_changes = true

This results in getting the first element in each window. Especially useful with a tumbling window.

Last

The last element of a window. See example below.

Name	Description	Default Value	Optional?
`OUTPUT_ATTRIBUTES`	The name for the output attribute.	`last`	True

You should use the following settings:

EVAL_AT_NEW_ELEMENT = false
EVAL_BEFORE_REMOVE_OUTDATING = true

This results in getting the last element in each window. Especially useful with a tumbling window.

Trigger The tuple that triggers the output. TODO

Variance Calculates the variance TODO (similar to Sum)

TopK Calculates the top-K list TODO

Nest Nests the valid elements as list. TODO

...

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