PreviousValue
Description
The PreviousValue node recalls a value that was captured during a previous occurrence of an event with a specific key. It allows you to access the last seen value of a given expression for each group of events defined by a grouping key.
Parameters and configuration
| Name | Description |
|---|---|
| Output variable name | This variable will contain the last value seen for the particular grouping key |
| Key by | One or more expressions that define how input events are grouped. The component keeps track of the last value separately for each unique combination of their values. Defaults to an empty list {}, so one value is kept for the whole stream. UI tip: After entering each Key by expression, press Enter to add it. To edit an existing expression, click it. |
| Value | The value to remember. It will be recalled when another event with the same grouping key arrives. |
Example
Given stream of events which contain users with their current location, when we set
- Key by as
#input.userId - Value as
#input.location
then the value of the output variable is the previous location for the current user. If this is the first appearance of this user, the current location will be returned.