lightgbm.train

lightgbm.train(params, train_set, num_boost_round=100, valid_sets=None, valid_names=None, fobj=None, feval=None, init_model=None, feature_name='auto', categorical_feature='auto', early_stopping_rounds=None, evals_result=None, verbose_eval='warn', learning_rates=None, keep_training_booster=False, callbacks=None)

Perform the training with given parameters.

Parameters

• params (dict) – Parameters for training.

• train_set (Dataset) – Data to be trained on.

• num_boost_round (int, optional (default=100)) – Number of boosting iterations.

• valid_sets (list of Dataset, or None, optional (default=None)) – List of data to be evaluated on during training.

• valid_names (list of str, or None, optional (default=None)) – Names of valid_sets.

• fobj (callable or None, optional (default=None)) –

  Customized objective function. Should accept two parameters: preds, train_data, and return (grad, hess).

  predslist or numpy 1-D array

  The predicted values. Predicted values are returned before any transformation, e.g. they are raw margin instead of probability of positive class for binary task.

  train_dataDataset

  The training dataset.

  gradlist or numpy 1-D array

  The value of the first order derivative (gradient) of the loss with respect to the elements of preds for each sample point.

  hesslist or numpy 1-D array

  The value of the second order derivative (Hessian) of the loss with respect to the elements of preds for each sample point.

  For multi-class task, the preds is group by class_id first, then group by row_id. If you want to get i-th row preds in j-th class, the access way is score[j * num_data + i] and you should group grad and hess in this way as well.

• feval (callable, list of callable, or None, optional (default=None)) –

  Customized evaluation function. Each evaluation function should accept two parameters: preds, train_data, and return (eval_name, eval_result, is_higher_better) or list of such tuples.

  predslist or numpy 1-D array

  The predicted values. If fobj is specified, predicted values are returned before any transformation, e.g. they are raw margin instead of probability of positive class for binary task in this case.

  train_dataDataset

  The training dataset.

  eval_namestr

  The name of evaluation function (without whitespaces).

  eval_resultfloat

  The eval result.

  is_higher_betterbool

  Is eval result higher better, e.g. AUC is is_higher_better.

  For multi-class task, the preds is group by class_id first, then group by row_id. If you want to get i-th row preds in j-th class, the access way is preds[j * num_data + i]. To ignore the default metric corresponding to the used objective, set the metric parameter to the string "None" in params.

• init_model (str, pathlib.Path, Booster or None, optional (default=None)) – Filename of LightGBM model or Booster instance used for continue training.

• feature_name (list of str, or 'auto', optional (default="auto")) – Feature names. If ‘auto’ and data is pandas DataFrame, data columns names are used.

• categorical_feature (list of str or int, or 'auto', optional (default="auto")) – Categorical features. If list of int, interpreted as indices. If list of str, interpreted as feature names (need to specify feature_name as well). If ‘auto’ and data is pandas DataFrame, pandas unordered categorical columns are used. All values in categorical features should be less than int32 max value (2147483647). Large values could be memory consuming. Consider using consecutive integers starting from zero. All negative values in categorical features will be treated as missing values. The output cannot be monotonically constrained with respect to a categorical feature.

• early_stopping_rounds (int or None, optional (default=None)) – Activates early stopping. The model will train until the validation score stops improving. Validation score needs to improve at least every early_stopping_rounds round(s) to continue training. Requires at least one validation data and one metric. If there’s more than one, will check all of them. But the training data is ignored anyway. To check only the first metric, set the first_metric_only parameter to True in params. The index of iteration that has the best performance will be saved in the best_iteration field if early stopping logic is enabled by setting early_stopping_rounds.

• evals_result (dict or None, optional (default=None)) –

  Dictionary used to store all evaluation results of all the items in valid_sets. This should be initialized outside of your call to train() and should be empty. Any initial contents of the dictionary will be deleted.

  Example

  With a valid_sets = [valid_set, train_set], valid_names = [‘eval’, ‘train’] and a params = {‘metric’: ‘logloss’} returns {‘train’: {‘logloss’: [‘0.48253’, ‘0.35953’, …]}, ‘eval’: {‘logloss’: [‘0.480385’, ‘0.357756’, …]}}.

• verbose_eval (bool or int, optional (default=True)) –

  Requires at least one validation data. If True, the eval metric on the valid set is printed at each boosting stage. If int, the eval metric on the valid set is printed at every verbose_eval boosting stage. The last boosting stage or the boosting stage found by using early_stopping_rounds is also printed.

  Example

  With verbose_eval = 4 and at least one item in valid_sets, an evaluation metric is printed every 4 (instead of 1) boosting stages.

• learning_rates (list, callable or None, optional (default=None)) – List of learning rates for each boosting round or a callable that calculates learning_rate in terms of current number of round (e.g. yields learning rate decay).

• keep_training_booster (bool, optional (default=False)) – Whether the returned Booster will be used to keep training. If False, the returned value will be converted into _InnerPredictor before returning. This means you won’t be able to use eval, eval_train or eval_valid methods of the returned Booster. When your model is very large and cause the memory error, you can try to set this param to True to avoid the model conversion performed during the internal call of model_to_string. You can still use _InnerPredictor as init_model for future continue training.

• callbacks (list of callable, or None, optional (default=None)) – List of callback functions that are applied at each iteration. See Callbacks in Python API for more information.

Returns

booster – The trained Booster model.

Return type

Booster