AWS Documentation » Amazon SageMaker » Developer Guide » Using Built-in Algorithms with Amazon SageMaker » XGBoost Algorithm

XGBoost Algorithm

XGBoost (eXtreme Gradient Boosting) is a popular and efficient open-source implementation of the gradient boosted trees algorithm. Gradient boosting is a supervised learning algorithm that attempts to accurately predict a target variable by combining the estimates of a set of simpler, weaker models. XGBoost has done remarkably well in machine learning competitions because to it robustly handles a variety of data types, relationships, and distributions, and the large number of hyperparameters that can be tweaked and tuned for improved fits. This flexibility makes XGBoost a solid choice for problems in regression, classification (binary and multiclass), and ranking.

Topics

• Input/Output Interface
• EC2 Instance Recommendation
• XGBoost Sample Notebooks
• How XGBoost Works
• XGBoost Hyperparameters
• Tuning a XGBoost Model

Input/Output Interface

Gradient boosting operates on tabular data, with the rows representing observations, one column representing the target variable or label, and the remaining columns representing features.

Amazon SageMaker’s implementation of XGBoost supports CSV and libsvm formats for training and inference:

• For Training ContentType, valid inputs are text/libsvm (default) or text/csv.

• For Inference ContentType, valid inputs are text/libsvm or text/csv.

Note

For CSV training, the algorithm assumes that the target variable is in the first column and that the CSV does not have a header record. For CSV inference, the algorithm assumes that CSV input does not have the label column.

For libsvm training, the algorithm assumes that the label is in the first column. Subsequent columns contain the index value pairs for features. So each row has the format: <label> <index1>:<value1> <index2>:<value2> ... Inference requests for libsvm may or may not have labels in the libsvm format.

This differs from other Amazon SageMaker algorithms, which use the protobuf training input format to maintain greater consistency with standard XGBoost data formats.

For CSV training input mode, the total memory available to the algorithm (Instance Count * the memory available in the InstanceType) must be able to hold the training dataset. For libsvm training input mode, it's not required, but we recommend it.

SageMaker XGBoost uses the Python pickle module to serialize/deserialize the model, which can be used for saving/loading the model.

To use a model trained with SageMaker XGBoost in open source XGBoost

• Use the following Python code:

  import pickle as pkl 
  model = pkl.load(open(model_file_path, 'rb'))
  # prediction with test data
  pred = model.predict(dtest)

To differentiate instance importance use Instance Weight Support

• Amazon SageMaker XGBoost allows customers to differentiate the importance of instances by assigning each instance a weight value. For text/libsvm input, customers can assign weight values to instances by attaching them after the labels. For example, label:weight idx_0:val_0 idx_1:val_1.... For text/csv input, customers need to turn on the csv_weights flag in the parameters and attach weight values in the column after labels. For example: label,weight,val_0,val_1,...).

EC2 Instance Recommendation

Amazon SageMaker XGBoost currently only trains using CPUs. It is a memory-bound (as opposed to compute-bound) algorithm. So, a general-purpose compute instance (for example, M4) is a better choice than a compute-optimized instance (for example, C4). Further, we recommend that you have enough total memory in selected instances to hold the training data. Although it supports the use of disk space to handle data that does not fit into main memory (the out-of-core feature available with the libsvm input mode), writing cache files onto disk slows the algorithm processing time.

XGBoost Sample Notebooks

For a sample notebook that shows how to use the Amazon SageMaker XGBoost algorithm to train and host a regression model, see Regression with Amazon SageMaker XGBoost algorithm. For instructions how to create and access Jupyter notebook instances that you can use to run the example in Amazon SageMaker, see Using Notebook Instances. Once you have created a notebook instance and opened it, select the SageMaker Examples tab to see a list of all the Amazon SageMaker samples. The topic modeling example notebooks using the NTM algorithms are located in the Introduction to Amazon algorithms section. To open a notebook, click on its Use tab and select Create copy.