def predict_prob(model, df, features):
    """Calculate prediciton probability

    Args:
        model (RandomForestClassifier): trained classifier
        df (pandas.DataFrame): validation dataframe
        features (list): a list of feature names
    Returns:
        prob (np.array): len(df)x3
    """
    X = df[features]
    prob = model.predict_proba(X)

    return prob