Savitzky-Golay Filter

This example covers the following:

• using BaseAlgo
• converting parameters
• using the prepare_features utility
• using an arbitrary function to transform data

In this example, you will add SciPy's implementation of a Savitzky-Golay signal processing filter to the Splunk Machine Learning Toolkit. See the SciPy documentation for details on the filter.

Since SciPy's savgol_filter is just a function, we will do all the work in the fit method and return the transformed values there.

This example uses the ML-SPL API available in the Splunk Machine Learning Toolkit version 2.2.0 and later. Verify your Splunk Machine Learning Toolkit version before using this example.

Steps

1. Register the algorithm in __init__.py.
   Modify the __init__.py file located in $SPLUNK_HOME/etc/apps/Splunk_ML_Toolkit/bin/algos to "register" your algorithm by adding it to the list here:

   __all__ = [
       "SavgolFilter",
       "LinearRegression",
       "Lasso",
       ...
       ]
   

2. Create the python file in the algos folder. For this example, we create $SPLUNK_HOME/etc/apps/Splunk_ML_Toolkit/bin/algos/SavgolFilter.py.
   

   import numpy as np
   from scipy.signal import savgol_filter
    
   from base import BaseAlgo
   from util.param_util import convert_params
   from util import df_util
   

3. Define the class.
   

   class SavgolFilter(BaseAlgo):
       """Use SciPy's savgol_filter to run a filter over fields."""
   

4. Define the __init__ method.
   Since there isn't an estimator class like other examples, attach the params to the object (self) to use later.

       def __init__(self, options):
           # set parameters
           params = options.get('params', {})
           out_params = convert_params(
               params,
               ints=['window_length', 'polyorder', 'deriv']
           )
   
           # set defaults for parameters
           if 'window_length' in out_params:
               self.window_length = out_params['window_length']
           else:
               self.window_length = 5
   
           if 'polyorder' in out_params:
               self.polyorder = out_params['polyorder']
           else:
   
               self.polyorder = 2
               if 'deriv' in out_params:
                   self.deriv = out_params['deriv']
               else:
                   self.deriv = 0
   

5. Define the fit method.
   

      def fit(self, df, options):
           X = df.copy()
           X, nans, columns = df_util.prepare_features(X, self.feature_variables)
    
   	# Define a wrapper function
           def f(x):
               return savgol_filter(x, self.window_length, self.polyorder, self.deriv)
    
   	# Apply that function along each column of X
           y_hat = np.apply_along_axis(f, 0, X)
    
           names = ['SG_%s' % col for col in columns]
           output_df = df_util.create_output_dataframe(y_hat, nans, names)
           df = df_util.merge_predictions(df, output_df)
    
           return df
   

   Finished example

   import numpy as np
   from scipy.signal import savgol_filter
   
   from base import BaseAlgo
   from util.param_util import convert_params
   from util import df_util
   
   
   class SavgolFilter(BaseAlgo):
   
       def __init__(self, options):
           # set parameters
           params = options.get('params', {})
           out_params = convert_params(
               params,
               ints=['window_length', 'polyorder', 'deriv']
           )
   
           # set defaults for parameters
           if 'window_length' in out_params:
               self.window_length = out_params['window_length']
           else:
               self.window_length = 5
   
           if 'polyorder' in out_params:
               self.polyorder = out_params['polyorder']
           else:
   
               self.polyorder = 2
               if 'deriv' in out_params:
                   self.deriv = out_params['deriv']
               else:
                   self.deriv = 0
   
       def fit(self, df, options):
           X = df.copy()
           X, nans, columns = df_util.prepare_features(X, self.feature_variables)
   
           def f(x):
               return savgol_filter(x, self.window_length, self.polyorder, self.deriv)
   
           y_hat = np.apply_along_axis(f, 0, X)
   
           names = ['SG_%s' % col for col in columns]
           output_df = df_util.create_output_dataframe(y_hat, nans, names)
           df = df_util.merge_predictions(df, output_df)
   
           return df