A generalization of the scikit-learn pipeline. Can evaluate directed graphs.
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Python Evaluator for Machine Learning Workflows

This project allows for the evaluation of whole machine learning workflows specified in a simple JSON format. As such, it can be considered an extension of the Pipeline class in scikit-learn. Moreover, it contains a simple XMLRPC interface which allows for parallel evaluation of a number of worflows at once.

The project originated as part of GP-ML, a framework for the automatic design of machine learning workflows based on genetic programming, where it was used for the evaluation of the population in a distributed way. The population is provided through the XMLRPC interface as a single JSON-formatted string which contains a list of workflows. Each workflow is a dictionary of methods indexed by (workflow-unique) identifiers. Each method is in turn described as a triple of (list of input IDs, method with parameters, list of output IDs).

Getting Started

To start using the project, you simply need to start the xmlrpc_interface.py script to start the server on localhost:8080.

python -m scoop xmlrpc_interface.py <log_path>

Once started, the server can be called through the XML-RPC and provides three basic functions

  1. get_param_sets(datafile) returns the set of parameters for all machine learning methods the server understands based on the input datafile (the ranges of parameters for some methods may change depending e.g. the number of attributes in the dataset)
  2. evaluate(json_string, datafile) evaluates the machine learning workflow described by the json_string (see below) on the datafile
  3. quit() stops the server

Format of the input JSON

The input JSON contains a list of machine learning worklows [wf_1, ..., wf_n] which should be evaluated on the same dataset. Each workflow in the list is a dictionary {"method1": method_spec1, "method2": method_spec2, ...} which contains the specification of at least two methods. Each method specification, in turn, is a triple [inputs, [method, parameters], outputs].

In each workflow, an input method must be specified, this method has no inputs, and is used only to rename the input file to an ID which is used in the rest of the workflow. For example, the following method specification tells the system that the input file will be referenced as "IN:0" in the rest of the workflow.

 "input" : [ [], "input", ["IN:0"] ],

The workflow further contains any number of other methods. Each method must provide the list of its inputs, its name and parameters and a list of outputs. There are methods of four types

  1. splitter is a methods which has a single input and provides a list of outputs, for example the k-means algorithm can be used to split the data into clusters
  2. transformer is a method with a single input and a single output which is used transform the data in any way, for example PCA analysis or feature selection can be performed with a splitter
  3. classifier/regressor is a method, which is capable of learning from the data and provides predictions for new data
  4. aggregator is a method with several inputs and a single output, this method is used to aggregate results from several classifiers or regressors, currently only voting is supported as an agreggator (however, the implementation of voting can be used to combine the results if the dataset was split into several smaller dataset)

Inputs and outputs of the methods are specified by unique IDs. These IDs only connect the outputs of one method to the inputs of other methods and their values do not affect the results in any way. The same holds for the keys of the methods in the dictionary. The only exception to this rule is the input method, which must have this name.

The last method in the workflow must contain an empty list of outputs, which signifies that the output its output is the output of the whole workflow.

Example specifications

Let's provide a few examples of workflow specifications.

A single method

This workflow contains only a single decision tree classifier with depth limited to 10 used on the input data directly.

  "input" : [ [], "input", ["IN:0"] ],
  "DT" : [ ["IN:0"], ["DT", {"max_depth": 10}], [] ]

Three methods and voting

This workflow contains a decision tree with maximum depth of 10, gaussian naive Bayes classifier, and a support vector classifier with the complexity constant set to 0.5. The results of these three methods are aggregated with voting.

  "input" : [ [], "input", ["IN:0"] ],
  "DT" : [ ["IN:0"], ["DT", {"max_depth": 10}], ["DT:0"] ],
  "GNB" : [ ["IN:0"], ["gaussianNB", {}], ["GNB:0"] ],
  "SVC" : [ ["IN:0"], ["SVC", {"C": 0.5}], ["SVC:0"] ],
  "vote" : [ ["DT:0", "GNB:0", "SVC:0"], ["vote", {}], [] ]

A more complex example

In this example, the data are first pre-processed using the PCA analysis and then split into two groups using the k-means clustering. The first group is classified using the support vector classifier, the other group is classified with a decision tree. The results of these two methods are merged back together with voting. Additionally, the raw data are also processed with another decision tree. Finally, voting is used to aggregate the results of the last split.

  "input" : [ [], "input", ["IN:0"] ],
  "PCA" : [ ["IN:0"], ["PCA", {"feat_frac": 0.1}], ["PCA:0"] ],
  "kMeans" : [ ["PCA:0"], ["kMeans", {}], ["kM:0", "kM:1"] ],
  "SVC" : [ ["kM:0"], ["SVC", {}], ["SVC:0"] ],
  "DT1" : [ ["kM:1"], ["DT", {}], ["DT1:0"] ],
  "vote1" : [ ["SVC:0", "DT1:0"], ["vote", {}], ["VT1:0"] ],
  "DT2" : [ ["IN:0"], ["DT", {}], ["DT2:0"] ],
  "vote2" : [ ["VT1:0", "DT2:0"], ["vote", {}], [] ]


  1. Python 3
  2. numpy, scipy, pandas, scikit-learn, matplotlib, scoop

How it works

Internally, the evaluator runs in iterations. In each iteration, it checks all the unprocessed methods and selects those that have all data available. These are then trained on their data. It essentially implements a simple topological sorting algorithm.

Add a new method

Adding new methods is simple for new machine learning methods, which implement the scikit-learn interface, just add the method to the model_names dictionary in method_params.py and add the possible values of its parameters to the create_param_set method.

For the feature selection methods, do the same, and additionally add the handling of the number of selected features to the train_dag method in eval.py. This currently cannot be handled automatically, as the methods require the number of features which is not known in advance (e.g. if such a method follows another feature selection methods). Therefore, the number of features is handled as a fraction during the parameter search and is transformed to the actual number during training.