Nkululeko: meta parameter optimization

With linear classifiers that are derived from sklearn, you can simply state your variants for a meta parameter in the ini file:

type = svm
tuning_params = ['C']
scoring = recall_macro
C = [10, 1, 0.1, 0.01, 0.001, 0.0001]

This will iterate the C parameter of the SVM classifier by the stated values and choose the best performing model.
You can have several "tuning_params" and them a grid search (combining everything with each other) will be performed.

Here's an example for XGB classifier:

type = xgb
tuning_params = ['subsample', 'n_estimators', 'max_depth']
subsample = [.5, .7]
n_estimators = [50, 80, 200]
max_depth = [1, 6]

Here's one idea how to find the optimal values for 2 layers of an MLP net with nkululeko:

  • store your meta-parameters in arrays
  • loop over them and initialize an experiment each time
  • keep the experiment name but change your parameters and the plot name
  • this way you can re-use your extracted features and do not get your harddisk cluttered.

Here's some python code to illustrate this idea:

def main(config_file):
    # load one configuration per experiment
    config = configparser.ConfigParser()
    util = Util()
    l1s = [32, 64, 128]
    l2s = [16, 32, 64]
    for l1 in l1s:
        for l2 in l2s:
            # create a new experiment
            expr = exp.Experiment(config)

            plotname = f'{util.get_exp_name()}_{l1}_{l2}'
            util.set_config_val('PLOT', 'name', plotname)

            print(f'running {expr.name} with layers {l1} and {l2}')

            layers = {'l1':l1, 'l2':l2}
            util.set_config_val('MODEL', 'layers', layers)

            # load the data

            # split into train and test
            util.debug(f'train shape : {expr.df_train.shape}, test shape:{expr.df_test.shape}')

            # extract features
            util.debug(f'train feats shape : {expr.feats_train.df.shape}, test feats shape:{expr.feats_test.df.shape}')

            # initialize a run manager

            # run the experiment


Keep in mind though that meta parameter optimization like done here is in itself a learning problem. It is usually not feasible to systematically try out all combinations of possible values and thus some kind of stochastic approach is preferable.

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