This callback is constructed with anonymous functions that will be called
at the appropriate time (during Model.{fit | evaluate | predict}).
Note that the callbacks expects positional arguments, as:
on_epoch_begin and on_epoch_end expect two positional arguments:
epoch, logs
on_train_begin and on_train_end expect one positional argument:
logs
on_train_batch_begin and on_train_batch_end expect two positional
arguments: batch, logs
See Callback class definition for the full list of functions and their
expected arguments.
callback_lambda(
on_epoch_begin = NULL,
on_epoch_end = NULL,
on_train_begin = NULL,
on_train_end = NULL,
on_train_batch_begin = NULL,
on_train_batch_end = NULL,
...
)A Callback instance that can be passed to fit.keras.src.models.model.Model().
called at the beginning of every epoch.
called at the end of every epoch.
called at the beginning of model training.
called at the end of model training.
called at the beginning of every train batch.
called at the end of every train batch.
Any function in Callback() that you want to override by
passing function_name = function. For example,
callback_lambda(.., on_train_end = train_end_fn). The custom function
needs to have same arguments as the ones defined in Callback().
# Print the batch number at the beginning of every batch.
batch_print_callback <- callback_lambda(
on_train_batch_begin = function(batch, logs) {
print(batch)
}
)# Stream the epoch loss to a file in new-line delimited JSON format
# (one valid JSON object per line)
json_log <- file('loss_log.json', open = 'wt')
json_logging_callback <- callback_lambda(
on_epoch_end = function(epoch, logs) {
jsonlite::write_json(
list(epoch = epoch, loss = logs$loss),
json_log,
append = TRUE
)
},
on_train_end = function(logs) {
close(json_log)
}
)
# Terminate some processes after having finished model training.
processes <- ...
cleanup_callback <- callback_lambda(
on_train_end = function(logs) {
for (p in processes) {
if (is_alive(p)) {
terminate(p)
}
}
}
)
model %>% fit(
...,
callbacks = list(
batch_print_callback,
json_logging_callback,
cleanup_callback
)
)
Other callbacks:
Callback()
callback_backup_and_restore()
callback_csv_logger()
callback_early_stopping()
callback_learning_rate_scheduler()
callback_model_checkpoint()
callback_reduce_lr_on_plateau()
callback_remote_monitor()
callback_swap_ema_weights()
callback_tensorboard()
callback_terminate_on_nan()