Gradient boosting algorithm is one of the most interesting and overlooked algorithm in machine learning. There are huge gaps between the simple theoretical formula and practical implementations, especially the histogram technique . The histogram-based feature representation not only greatly improves the speed, but also improves the accuracy. In some sense, the histogram is a sparse embedding technique, which map the noisy feature to a more compact and more robust space. And we could get more along this direction. Based on the deep understanding of feature embedding technique, we present LiteMORT, which use much less memory than other GBDT libs. It also has higher accuracy in some datasets. LiteMORT reveals that GBDT algorithm can have much more potential than most people would expect.

For example , in the latest Kaggle competition IEEE-CIS Fraud Detection competition (binary classification problem) :

1） LiteMORT is much faster than LightGBM. LiteMORT needs only a quarter of the time of LightGBM.

2）LiteMORT has higher auc than LightGBM.

For the detail comparison of this competition, please see https://github.com/closest-git/ieee_fraud.

1. Share memory with data source (pandas dataframe, numpy ndarray, list, vector… )

LiteMORT would not allocate extra memory for features stored in continuous memory. In the gradient boosting process, nearly all visit to data is on the pointer and some offsets.

2. Implicit merging for “merge overflow problem”

In real application, we usually don’t save all the data in one big data table. They are always many smaller ones instead. But in the data analysis or machine learning task, we have to access all datas. Or we have to merge some small datasets to get some huge datasets, which are too huge to be processed by many classical machine learning algorithms. We called this phenomenon as “merge overflow problem”. LiteMORT use a smart implicit merging technique to deal with this problem. Just send all small datasets to LiteMORT, LiteMORT would generate the histograms for each merged features. In the later training process, all operations are on these histograms. No need to generate the huge merged dataset as the classical method or other GBDT libs(LightGBM, XGBoost,...)

from litemort import *
mode = LiteMORT(params).fit(train_x, train_y, eval_set=[(eval_x, eval_y)])
pred_val = model.predict(eval_x)
pred_raw = model.predict_raw(eval_x)

Support parameters of LightGBM

As shown below, just one more line to transform from lightGBM to LiteMORT.

if model_type == 'mort':
    model = LiteMORT(params).fit_1(X_train, y_train, eval_set=[(X_valid, y_valid)])
if model_type == 'lgb':
    model = lgb.LGBMRegressor(**params, n_jobs=-1)
    model.fit(X_train, y_train, eval_set=[(X_train, y_train), (X_valid, y_valid)])
pred_test = model.predict(X_test)

Please use the following bibtex entry:

[1] Chen, Yingshi."LiteMORT: A memory efficient gradient boosting tree system on adaptive compact distributions." arXiv preprint arXiv:2001.09419 (2020).

LiteMORT was written by Yingshi Chen (gsp.cys@gmail.com)