llama (version 0.9.2)

llama-package: Leveraging Learning to Automatically Manage Algorithms

Description

Leveraging Learning to Automatically Manage Algorithms provides functionality to read and process performance data for algorithms, facilitate building models that predict which algorithm to use in which scenario and ways of evaluating them.

Details

The package provides functions to read performance data, build performance models that enable selection of algorithms (using external machine learning functions) and evaluate those models.

Data is input using input and can then be used to learn performance models. There are currently four main ways to create models. Classification (classify) creates a single machine learning model that predicts the algorithm to use as a label. Classification of pairs of algorithms (classifyPairs) creates a classification model for each pair of algorithms that predicts which one is better and aggregates these predictions to determine the best overall algorithm. Clustering (cluster) clusters the problems to solve and assigns the best algorithm to each cluster. Regression (regression) trains separate models for all available algorithms, predicts the performance on a problem independently and chooses the algorithm with the best predicted performance. Regression of pairs of algorithms (regressionPairs) is similar to classifyPairs, but predicts the performance difference between each pair of algorithms.

Various functions to split the data into training and test set(s) and to evaluate the performance of the learned models are provided.

LLAMA uses the mlr package to access the implementation of machine learning algorithms in R.

The model building functions are using the parallelMap package (https://github.com/berndbischl/parallelMap) to parallelize across the data partitions (e.g. cross-validation folds) with level "llama.fold" and "llama.tune" for tuning. By default, everything is run sequentially. By loading a suitable backend (e.g. through parallelStartSocket(2) for parallelization across 2 CPUs using sockets), the model building will be parallelized automatically and transparently. Note that this does not mean that all machine learning algorithms used for building models can be parallelized safely. For functions that are not thread safe, use parallelStartSocket to run in separate processes.

References

Kotthoff, L. (2013) LLAMA: Leveraging Learning to Automatically Manage Algorithms. arXiv:1306.1031.

Kotthoff, L. (2014) Algorithm Selection for Combinatorial Search Problems: A survey. AI Magazine.

Examples

# NOT RUN {
if(Sys.getenv("RUN_EXPENSIVE") == "true") {
data(satsolvers)
folds = cvFolds(satsolvers)

model = classify(classifier=makeLearner("classif.J48"), data=folds)
# print the total number of successes
print(sum(successes(folds, model)))
# print the total misclassification penalty
print(sum(misclassificationPenalties(folds, model)))
# print the total PAR10 score
print(sum(parscores(folds, model)))

# number of total successes for virtual best solver for comparison
print(sum(successes(satsolvers, vbs, addCosts = FALSE)))

# print predictions on the entire data set
print(model$predictor(subset(satsolvers$data, TRUE, satsolvers$features)))

# train a regression model
model = regression(regressor=makeLearner("regr.lm"), data=folds)
# print the total number of successes
print(sum(successes(folds, model)))
}
# }