arbok

Arbok

Arbok (A\ utoml w\ r\ apper tool\ b\ ox for o\ penml c\ ompatibility) provides wrappers for TPOT and Auto-Sklearn, as a compatibility layer between these tools and OpenML.

The wrapper extends Sklearn’s BaseSearchCV and provides all the internal parameters that OpenML needs, such as cv_results_, best_index_, best_params_, best_score_ and classes_.

Installation

::

pip install arbok

Simple example

.. code:: python

import openml
from arbok import AutoSklearnWrapper, TPOTWrapper


task = openml.tasks.get_task(31)
dataset = task.get_dataset()

# Get the AutoSklearn wrapper and pass parameters like you would to AutoSklearn
clf = AutoSklearnWrapper(
    time_left_for_this_task=3600, per_run_time_limit=360
)

# Or get the TPOT wrapper and pass parameters like you would to TPOT
clf = TPOTWrapper(
    generations=100, population_size=100, verbosity=2
)

# Execute the task
run = openml.runs.run_model_on_task(task, clf)
run.publish()

print('URL for run: %s/run/%d' % (openml.config.server, run.run_id))

Preprocessing data

To make the wrapper more robust, we need to preprocess the data. We can fill the missing values, and one-hot encode categorical data.

First, we get a mask that tells us whether a feature is a categorical feature or not.

.. code:: python

dataset = task.get_dataset()
_, categorical = dataset.get_data(return_categorical_indicator=True)
categorical = categorical[:-1]  # Remove last index (which is the class)

Next, we setup a pipeline for the preprocessing. We are using a ConditionalImputer, which is an imputer which is able to use different strategies for categorical (nominal) and numerical data.

.. code:: python

from sklearn.pipeline import make_pipeline
from sklearn.preprocessing import OneHotEncoder
from arbok import ConditionalImputer

preprocessor = make_pipeline(

    ConditionalImputer(
        categorical_features=categorical,
        strategy="mean",
        strategy_nominal="most_frequent"
    ),

    OneHotEncoder(
        categorical_features=categorical, handle_unknown="ignore", sparse=False
    )
)

And finally, we put everything together in one of the wrappers.

.. code:: python

clf = AutoSklearnWrapper(
    preprocessor=preprocessor, time_left_for_this_task=3600, per_run_time_limit=360
)

Limitations

-  Currently only the classifiers are implemented. Regression is
   therefore not possible.
-  For TPOT, the ``config_dict`` variable can not be set, because this
   causes problems with the API.

Benchmarking
------------

Installing the ``arbok`` package includes the ``arbench`` cli tool. We
can generate a json file like this:

.. code:: python

    from arbok.bench import Benchmark
    bench = Benchmark()
    config_file = bench.create_config_file(

        # Wrapper parameters
        wrapper={"refit": True, "verbose": False, "retry_on_error": True},

        # TPOT parameters
        tpot={
            "max_time_mins": 6,              # Max total time in minutes
            "max_eval_time_mins": 1          # Max time per candidate in minutes
        },

        # Autosklearn parameters
        autosklearn={
            "time_left_for_this_task": 360,  # Max total time in seconds
            "per_run_time_limit": 60         # Max time per candidate in seconds
        }
    )

And then, we can call arbench like this:

.. code:: bash

    arbench --classifier autosklearn --task-id 31 --config config.json

Or calling arbok as a python module:

.. code:: bash

    python -m arbok --classifier autosklearn --task-id 31 --config config.json

Running a benchmark on batch systems
------------------------------------

To run a large scale benchmark, we can create a configuration file like
above, and generate and submit jobs to a batch system as follows.

.. code:: python

    # We create a benchmark setup where we specify the headers, the interpreter we
    # want to use, the directory to where we store the jobs (.sh-files), and we give
    # it the config-file we created earlier.
    bench = Benchmark(
        headers="#PBS -lnodes=1:cpu3\n#PBS -lwalltime=1:30:00",
        python_interpreter="python3",  # Path to interpreter
        root="/path/to/project/",
        jobs_dir="jobs",
        config_file="config.json",
        log_file="log.json"
    )

    # Create the config file like we did in the section above
    config_file = bench.create_config_file(

        # Wrapper parameters
        wrapper={"refit": True, "verbose": False, "retry_on_error": True},

        # TPOT parameters
        tpot={
            "max_time_mins": 6,              # Max total time in minutes
            "max_eval_time_mins": 1          # Max time per candidate in minutes
        },

        # Autosklearn parameters
        autosklearn={
            "time_left_for_this_task": 360,  # Max total time in seconds
            "per_run_time_limit": 60         # Max time per candidate in seconds
        }
    )

    # Next, we load the tasks we want to benchmark on from OpenML.
    # In this case, we load a list of task id's from study 99.
    tasks = openml.study.get_study(99).tasks

    # Next, we create jobs for both tpot and autosklearn.
    bench.create_jobs(tasks, classifiers=["tpot", "autosklearn"])

    # And finally, we submit the jobs using qsub
    bench.submit_jobs()

Preprocessing parameters
------------------------

.. code:: python

    from arbok import ParamPreprocessor
    import numpy as np
    from sklearn.feature_selection import VarianceThreshold
    from sklearn.pipeline import make_pipeline

    X = np.array([
        [1, 2, True, "foo", "one"],
        [1, 3, False, "bar", "two"],
        [np.nan, "bar", None, None, "three"],
        [1, 7, 0, "zip", "four"],
        [1, 9, 1, "foo", "five"],
        [1, 10, 0.1, "zip", "six"]
    ], dtype=object)

    # Manually specify types, or use types="detect" to automatically detect types
    types = ["numeric", "mixed", "bool", "nominal", "nominal"]

    pipeline = make_pipeline(ParamPreprocessor(types="detect"), VarianceThreshold())

    pipeline.fit_transform(X)

Output:

::

    [[-0.4472136  -0.4472136   1.41421356 -0.70710678 -0.4472136  -0.4472136
       2.23606798 -0.4472136  -0.4472136  -0.4472136   0.4472136  -0.4472136
      -0.85226648  1.        ]
     [-0.4472136   2.23606798 -0.70710678 -0.70710678 -0.4472136  -0.4472136
      -0.4472136  -0.4472136  -0.4472136   2.23606798  0.4472136  -0.4472136
      -0.5831297  -1.        ]
     [ 2.23606798 -0.4472136  -0.70710678 -0.70710678 -0.4472136  -0.4472136
      -0.4472136  -0.4472136   2.23606798 -0.4472136  -2.23606798  2.23606798
      -1.39054004 -1.        ]
     [-0.4472136  -0.4472136  -0.70710678  1.41421356 -0.4472136   2.23606798
      -0.4472136  -0.4472136  -0.4472136  -0.4472136   0.4472136  -0.4472136
       0.49341743 -1.        ]
     [-0.4472136  -0.4472136   1.41421356 -0.70710678  2.23606798 -0.4472136
      -0.4472136  -0.4472136  -0.4472136  -0.4472136   0.4472136  -0.4472136
       1.031691    1.        ]
     [-0.4472136  -0.4472136  -0.70710678  1.41421356 -0.4472136  -0.4472136
      -0.4472136   2.23606798 -0.4472136  -0.4472136   0.4472136  -0.4472136
       1.30082778  1.        ]]