The change_detect node
Emits new point-values only if different from the previous point.
- Multiple fields can be monitored for change by this node.
- If no fields are given, the complete data-item is compared to the last one.
- If a reset_timeout is given, all previous values will be reset when no value is received within this amount of time. So that after the timeout the first data_item will be emitted.
- For value comparison erlang's strict equals (=:=) is used, so 1.0 is not equal to 1.
Example
%% detects any changes in data_items
|change_detect()
%% detect changes in one field, with timeout
%% outputs at least the first data_item coming in after a 3 second timeout
|change_detect('val')
.reset_timeout(3s)
%% detect changes in two fields, with timeout
|change_detect('data.State.Err', 'data.State.Msg')
.reset_timeout(60s)
% in-example json notation:
% {"data": {"x": {"temp": 32.4564}, "y" : {"temp" : 31.15155}} }
|change_detect('data.x.temp', 'data.y.temp')
Parameters
| Parameter | Description | Default |
|---|---|---|
[node] fields( string_list ) |
List of fields to monitor | undefined |
reset_timeout( duration ) |
Previous values TTL | 3h |
group_by( string ) |
Group the internal buffer by the value of this field, so that for every different value of it holds its own last value. | undefined |
strict( boolean ) |
If fields are given, when strict is set to true, all values have to change in order for the node to let a data_point pass. This has no effect, when fields is not given. |
true |