EventFilters specify arbitrarily complex logic for whether or not a LogEvent should be processed by a Logger or Appender. They are attached to Loggers/Appenders via their $set_filter() or $add_filter() methods. If any EventFilter evaluates to FALSE for a given event, that event is ignored - similarly to when it does not pass the objects' threshold.

Usually you do not need to instantiate a formal EventFilter object as you can just use any function that has the single argument event instead. If you need to implement more complex filter logic - for example a filter that is dependent on a dataset - it might be desirable to subclass EventFilter, as R6::R6 objects can store data and functions together.

.obj() is a special function that can only be used within the $filter() methods of EventFilters. It returns the Logger or Appender that the EventFilter is attached to.


Modifying LogEvents with EventFilters

Since LogEvents are R6 objects with reference semantics, EventFilters can be abused to modify events before passing them on. lgr comes with a few preset filters that use this property: FilterInject (similar to with_log_level()) and FilterForceLevel (similar to with_log_value()).

NOTE: The base class for Filters is called EventFilter so that it doesn't conflict with base::Filter(). The recommended convention for Filter subclasses is to call them FilterSomething and leave out the Event prefix.

See also


Public methods

Method new()

Initialize a new EventFilter


EventFilter$new(fun = function(event) TRUE)



a function with a single argument event that must return either TRUE or FALSE. Any non-FALSE will be interpreted as TRUE (= no filtering takes place) and a warning will be thrown.

Method clone()

The objects of this class are cloneable with this method.


EventFilter$clone(deep = FALSE)



Whether to make a deep clone.


lg <- get_logger("test") f <- function(event) { cat("via event$.logger:", event$.logger$threshold, "\n") # works for loggers only cat("via .obj(): ",.obj()$threshold, "\n") # works for loggers and appenders TRUE } lg$add_filter(f) lg$fatal("test")
#> via event$.logger: 400 #> via .obj(): 400 #> FATAL [08:07:52.998] test
#> <Logger> [info] test #> #> inherited appenders: #> console: <AppenderConsole> [all] -> console