lgb.train {lightgbm}

Main training logic for LightGBM

Description

Low-level R interface to train a LightGBM model. Unlike lightgbm, this function is focused on performance (e.g. speed, memory efficiency). It is also less likely to have breaking API changes in new releases than lightgbm.

Usage

lgb.train(
  params = list(),
  data,
  nrounds = 100L,
  valids = list(),
  obj = NULL,
  eval = NULL,
  verbose = 1L,
  record = TRUE,
  eval_freq = 1L,
  init_model = NULL,
  colnames = NULL,
  categorical_feature = NULL,
  early_stopping_rounds = NULL,
  callbacks = list(),
  reset_data = FALSE,
  serializable = TRUE
)

Arguments

params

a list of parameters. See the "Parameters" section of the documentation for a list of parameters and valid values.

data

a lgb.Dataset object, used for training. Some functions, such as lgb.cv, may allow you to pass other types of data like matrix and then separately supply label as a keyword argument.

nrounds

number of training rounds

valids

a list of lgb.Dataset objects, used for validation

obj

objective function, can be character or custom objective function. Examples include regression, regression_l1, huber, binary, lambdarank, multiclass, multiclass

eval

evaluation function(s). This can be a character vector, function, or list with a mixture of strings and functions.

• a. character vector: If you provide a character vector to this argument, it should contain strings with valid evaluation metrics. See The "metric" section of the documentation for a list of valid metrics.

• b. function: You can provide a custom evaluation function. This should accept the keyword arguments preds and dtrain and should return a named list with three elements:

  • name: A string with the name of the metric, used for printing and storing results.

  • value: A single number indicating the value of the metric for the given predictions and true values

  • higher_better: A boolean indicating whether higher values indicate a better fit. For example, this would be FALSE for metrics like MAE or RMSE.

• c. list: If a list is given, it should only contain character vectors and functions. These should follow the requirements from the descriptions above.

verbose

verbosity for output, if <= 0 and valids has been provided, also will disable the printing of evaluation during training

record

Boolean, TRUE will record iteration message to booster$record_evals

eval_freq

evaluation output frequency, only effective when verbose > 0 and valids has been provided

init_model

path of model file or lgb.Booster object, will continue training from this model

colnames

Deprecated. See "Deprecated Arguments" section below.

categorical_feature

Deprecated. See "Deprecated Arguments" section below.

early_stopping_rounds

int. Activates early stopping. When this parameter is non-null, training will stop if the evaluation of any metric on any validation set fails to improve for early_stopping_rounds consecutive boosting rounds. If training stops early, the returned model will have attribute best_iter set to the iteration number of the best iteration.

callbacks

List of callback functions that are applied at each iteration.

reset_data

Boolean, setting it to TRUE (not the default value) will transform the booster model into a predictor model which frees up memory and the original datasets

serializable

whether to make the resulting objects serializable through functions such as save or saveRDS (see section "Model serialization").

Value

a trained booster model lgb.Booster.

Deprecated Arguments

A future release of lightgbm will remove support for passing arguments 'categorical_feature' and 'colnames'. Pass those things to lgb.Dataset instead.

Early Stopping

"early stopping" refers to stopping the training process if the model's performance on a given validation set does not improve for several consecutive iterations.

If multiple arguments are given to eval, their order will be preserved. If you enable early stopping by setting early_stopping_rounds in params, by default all metrics will be considered for early stopping.

If you want to only consider the first metric for early stopping, pass first_metric_only = TRUE in params. Note that if you also specify metric in params, that metric will be considered the "first" one. If you omit metric, a default metric will be used based on your choice for the parameter obj (keyword argument) or objective (passed into params).

Examples

data(agaricus.train, package = "lightgbm")
train <- agaricus.train
dtrain <- lgb.Dataset(train$data, label = train$label)
data(agaricus.test, package = "lightgbm")
test <- agaricus.test
dtest <- lgb.Dataset.create.valid(dtrain, test$data, label = test$label)
params <- list(
  objective = "regression"
  , metric = "l2"
  , min_data = 1L
  , learning_rate = 1.0
  , num_threads = 2L
)
valids <- list(test = dtest)
model <- lgb.train(
  params = params
  , data = dtrain
  , nrounds = 5L
  , valids = valids
  , early_stopping_rounds = 3L
)