Adding Custom Features to Your Model

The features given to the model can often be the deciding factor for how well a model can produce accurate predictions. This is arguably even more so when approaching the problem using a method such as Active Learning, where you may only be using a tiny fraction of your entire dataset.

Custom Features

Custom generated features can be added as a new function to astronomicAL.extensions.feature_generation.

There are some requirements when declaring a new feature generation function:

  1. The new function must have two input parameters:

  • df - The DataFrame containing the entire dataset.

  • n - The number of features involved in the operation.

Note

If your particular operation does not easily scale to more than two features at a time, then you can simply not make use of the n input parameter inside your function. However you must still include n as an input parameter, even if you don’t use it.

  1. The function must return the following:

  • df - The updated dataframe with the newly generated features.

  • generated_features - a list containing the updated column names.

  1. The created function must be added as a new value to the oper dictionary within the get_oper_dict function, with a brief string key identifying the operation.

Within the function, you can generate the combinations of features using:

1base_features = config.settings["features_for_training"]
2combs = list(combinations(base_features, n))

Creating Colours

Given the prevalence of photometry data in astronomical datasets, the most common additional features to create are colours. In AstronomicAL, these are provided with the default subtract (a-b) with a combination value of 2.

Example: Max(a, b)

In this example, we will show how we would create a new max function. Although the produced features from this specific function may not be particularly useful for improving this model’s performance, it works well as an example.

 1def max_oper(df, n): # The function must include the parameters df and n
 2
 3    np.random.seed(0) # set random seed if required for reproducability
 4
 5    base_features = config.settings["features_for_training"] # get the base features chosen by the user
 6
 7    combs = list(combinations(base_features, n)) # a list of all the combinations of n base_features
 8
 9    cols = list(df.columns) # all the columns in the dataset
10    generated_features = [] # The list that will keep track of all the new feature names
11
12    for comb in combs: #loop over all combination tuples
13
14        # This loop is to create the feature name string for the dataframe
15        new_feature_name = "max(" # start of feature name
16        for i in range(n): # loop over each feature in tuple
17            new_feature_name = new_feature_name + f"{comb[i]}" # add each feature in operation
18            if i != (n - 1):
19                new_feature_name = new_feature_name + "," # seperate features by a comma
20            else:
21                new_feature_name = new_feature_name + ")"
22
23        generated_features.append(new_feature_name) # add new feature name which is the form: max(f_1,f_2,...,f_n)
24
25
26        if new_feature_name not in cols: # if the feature already exists in the data, dont recalculate
27
28            # This loop applies the operation over all the feature in the combination and adds it as the new column in the dataframe
29            for i in range(n): # Loop of each individual feature in comb
30                if i == 0:
31                    df[new_feature_name] = df[comb[i]] # add the new column and set its value to the starting feature (without this you will get a KeyError)
32                else:
33                    df[new_feature_name] = np.maximum(df[new_feature_name], df[comb[i]]) #calculate the running maximum
34
35    return df, generated_features  # The function must return the updated dataframe and the list of generated features

Finally, adding the new entry in the oper dictionary, without specifying the parameters:

def get_oper_dict():

    oper = {
        "subtract (a-b)": subtract,
        "add (a+b)": add,
        "multiply (a*b)": multiply,
        "divide (a/b)": divide,
        "max(a,b)": max_oper, # Newly created function
    }

    return oper

And that is all that is required. The new max_oper function is now available to use in AstronomicAL:

../../_images/create_feature_comb_list_max.png