Custom Parameters

Parameters unique to the Silverkite algorithm are included under model_components.custom.

Tip

Refer to this section for customizing Silverkite model. model_components.custom is currently not supported for Prophet.

custom = dict(
    fit_algorithm_dict=fit_algorithm_dict,
    feature_sets_enabled=feature_sets_enabled,
    max_daily_seas_interaction_order=max_daily_seas_interaction_order,
    max_weekly_seas_interaction_order=max_weekly_seas_interaction_order,
    extra_pred_cols=extra_pred_cols,
    drop_pred_cols=drop_pred_cols,
    explicit_pred_cols=explicit_pred_cols,
    min_admissible_value=min_admissible_value,
    max_admissible_value=max_admissible_value,
)

Fit algorithm

Silverkite abstracts feature creation from model fitting. First, Silverkite generates features for forecasting, using time-series domain knowledge. Then, any standard algorithm can be applied for fitting.

Silverkite supports the following algorithms from scikit-learn and statsmodels:

Silverkite fitting algorithms

fit_algorithm	class	notes
linear	statsmodels.regression.linear_model.OLS	More stable than sklearn.linear_model.LinearRegression
elastic_net	ElasticNetCV
ridge	RidgeCV
lasso	LassoCV
sgd	SGDRegressor	Default penalty = ‘l2’, alpha = 1e-4
lars	LarsCV
lasso_lars	LassoLarsCV
rf	RandomForestRegressor	Tree methods cannot capture growth
gradient_boosting	GradientBoostingRegressor	Supports quantile loss, tree methods cannot capture growth

You can select the algorithm via fit_algorithm and set its initialization parameters via fit_algorithm_params.

fit_algorithm_dict : `dict` or a list of such values for grid search
    How to fit the model. A dictionary with the following optional keys.

    ``"fit_algorithm"`` : `str`, default "ridge"
        The type of model used in fitting
        (implemented by sklearn and statsmodels).

        Available models are:

            - "statsmodels_ols"   : `statsmodels.regression.linear_model.OLS`
            - "statsmodels_wls"   : `statsmodels.regression.linear_model.WLS`
            - "statsmodels_gls"   : `statsmodels.regression.linear_model.GLS`
            - "statsmodels_glm"   : `statsmodels.genmod.generalized_linear_model.GLM`
            - "linear"            : `statsmodels.regression.linear_model.OLS`
            - "elastic_net"       : `sklearn.linear_model.ElasticNetCV`
            - "ridge"             : `sklearn.linear_model.RidgeCV`
            - "lasso"             : `sklearn.linear_model.LassoCV`
            - "sgd"               : `sklearn.linear_model.SGDRegressor`
            - "lars"              : `sklearn.linear_model.LarsCV`
            - "lasso_lars"        : `sklearn.linear_model.LassoLarsCV`
            - "rf"                : `sklearn.ensemble.RandomForestRegressor`
            - "gradient_boosting" : `sklearn.ensemble.GradientBoostingRegressor`

        See `~greykite.algo.common.ml_models.fit_model_via_design_matrix`
        for the sklearn and statsmodels classes that implement these methods, and their parameters.

        "linear" is the same as "statsmodels_ols", because `statsmodels.regression.linear_model.OLS`
        is more stable than `sklearn.linear_model.LinearRegression`.
    ``"fit_algorithm_params"`` : `dict` or None, default None (ridge penalty with alpha=1e-4)
        Parameters passed to the requested fit algorithm.
        If None, uses the defaults in `~greykite.algo.common.ml_models.fit_model_via_design_matrix`.

Examples:

custom = dict(
    fit_algorithm_dict=dict(
        fit_algorithm="linear"
    )
)

custom = dict(
    fit_algorithm_dict=dict(
        fit_algorithm="ridge",
        fit_algorithm_params={
            "alphas": 20
        }
    )
)

custom = dict(
    fit_algorithm_dict=dict(
        fit_algorithm="lasso_lars",
        fit_algorithm_params={
            "max_n_alphas": 100,
            "eps": 1e-2,
            "cv": 2
        }
    )
)

# Example using `sgd`. Note that `sgd` is often unstable.
# Consider using `ridge`, `lasso`, `elastic_net` instead.
custom = dict(
    fit_algorithm_dict=dict(
        fit_algorithm="sgd",
        fit_algorithm_params=dict(
            penalty="elasticnet",
            alpha=0.01,
            l1_ratio=0.2
        )
    )
)

# Grid search is possible
custom = dict(
    fit_algorithm_dict=[
        dict(
            fit_algorithm="linear"
        ),
        dict(
            fit_algorithm="ridge",
            fit_algorithm_params={
                "alphas": 20
            }
        ),
    ]
)

Note

“linear” is a good starting point. Sometimes the fit can be numerically unstable if you request holidays that don’t appear in your dataset. In that case, try “ridge” or “sgd”.

Interactions

You can include interactions via the feature_sets_enabled parameter. Setting feature_sets_enabled="auto" adds interactions appropriate to the data frequency and amount of training history.

The fourier order of seasonality interaction terms can be capped by max_daily_seas_interaction_order and max_weekly_seas_interaction_order for daily and weekly seasonality, respectively.

Options (defaults shown for SILVERKITE template):

feature_sets_enabled : `dict` [`str`, `bool` or "auto" or None] or `bool` or "auto" or None; or a list of such values for grid search, default "auto"
    Whether to include interaction terms and categorical variables to increase model flexibility.

    If a `dict`, boolean values indicate whether include various sets of features in the model.
    The following keys are recognized
    (from `~greykite.algo.forecast.silverkite.constants.silverkite_column.SilverkiteColumn`):

        ``"COLS_HOUR_OF_WEEK"`` : `str`
            Constant hour of week effect
        ``"COLS_WEEKEND_SEAS"`` : `str`
            Daily seasonality interaction with is_weekend
        ``"COLS_DAY_OF_WEEK_SEAS"`` : `str`
            Daily seasonality interaction with day of week
        ``"COLS_TREND_DAILY_SEAS"`` : `str`
            Allow daily seasonality to change over time by is_weekend
        ``"COLS_EVENT_SEAS"`` : `str`
            Allow sub-daily event effects
        ``"COLS_EVENT_WEEKEND_SEAS"`` : `str`
            Allow sub-daily event effect to interact with is_weekend
        ``"COLS_DAY_OF_WEEK"`` : `str`
            Constant day of week effect
        ``"COLS_TREND_WEEKEND"`` : `str`
            Allow trend (growth, changepoints) to interact with is_weekend
        ``"COLS_TREND_DAY_OF_WEEK"`` : `str`
            Allow trend to interact with day of week
        ``"COLS_TREND_WEEKLY_SEAS"`` : `str`
            Allow weekly seasonality to change over time

    The following dictionary values are recognized:

        - True: include the feature set in the model
        - False: do not include the feature set in the model
        - None: do not include the feature set in the model
        - "auto" or not provided: use the default setting based on data frequency and size

    If not a `dict`:

        - if a boolean, equivalent to a dictionary with all values set to the boolean.
        - if None, equivalent to a dictionary with all values set to False.
        - if "auto", equivalent to a dictionary with all values set to "auto".

max_daily_seas_interaction_order : `int` or None or a list of such values for grid search, default 5
    Max fourier order to use for interactions with daily seasonality
    (COLS_EVENT_SEAS, COLS_EVENT_WEEKEND_SEAS, COLS_WEEKEND_SEAS, COLS_DAY_OF_WEEK_SEAS, COLS_TREND_DAILY_SEAS).

    Model includes interactions terms specified by ``feature_sets_enabled``
    up to the order limited by this value and the available order from ``seasonality``.

max_weekly_seas_interaction_order : `int` or None or a list of such values for grid search, default 2
    Max fourier order to use for interactions with weekly seasonality (COLS_TREND_WEEKLY_SEAS).

    Model includes interactions terms specified by ``feature_sets_enabled``
    up to the order limited by this value and the available order from ``seasonality``.

when to use each feature set

feature set	max freq	when to use	(human-readable) formula
COLS_HOUR_OF_WEEK	hourly	hour of week effect to help daily seasonality model	hour_of_week
COLS_WEEKEND_SEAS	hourly	weekend has a different daily seasonality pattern	is_weekend:daily_seas
COLS_DAY_OF_WEEK_SEAS	hourly	each day has a different daily seasonality pattern	day_of_week:daily_seas
COLS_TREND_DAILY_SEAS	hourly	daily seasonality pattern changes over time, by is_weekend	trend:is_weekend:daily_seas
COLS_EVENT_SEAS	hourly	events have a different daily seasonality pattern	event:daily_seas
COLS_EVENT_WEEKEND_SEAS	hourly	events have a different daily event seasonality pattern, by is_weekend	event:is_weekend:daily_seas
COLS_DAY_OF_WEEK	daily	day of week effect to help weekly seasonality model	day_of_week
COLS_TREND_WEEKEND	daily	growth rate differs for weekend/weekday	trend:is_weekend
COLS_TREND_DAY_OF_WEEK	daily	growth rate differs by day of week	trend:day_of_week
COLS_TREND_WEEKLY_SEAS	daily	weekly seasonality pattern changes over time	trend:weekly_seas

Examples:

from greykite.algo.forecast.silverkite.constants.silverkite_column import SilverkiteColumn

# Uses the default for all feature sets based on data frequency and size (training data)
custom = dict(
    feature_sets_enabled="auto"
)
# Turns off all feature sets
custom = dict(
    feature_sets_enabled=False
)
custom = dict(
    feature_sets_enabled=None  # same as False (prefer False to be explicit)
)

# Turns on all feature sets
# (Not recommended. Use "auto" to enable all relevant feature sets, or
#  enable specific feature sets as shown below.)
custom = dict(
    feature_sets_enabled=True
)
# Turns on specific feature sets
custom = dict(
    feature_sets_enabled={
        # Not included in the model.
        SilverkiteColumn.COLS_HOUR_OF_WEEK: False,
        SilverkiteColumn.COLS_WEEKEND_SEAS: False,
        SilverkiteColumn.COLS_DAY_OF_WEEK_SEAS: False,
        SilverkiteColumn.COLS_TREND_DAILY_SEAS: False,
        SilverkiteColumn.COLS_EVENT_SEAS: False,
        # None is the same as False (prefer False to be explicit)
        SilverkiteColumn.COLS_EVENT_WEEKEND_SEAS: None,
        # Included in the model.
        SilverkiteColumn.COLS_DAY_OF_WEEK: True,
        SilverkiteColumn.COLS_TREND_WEEKEND: True,
        # Auto uses the default based on data frequency and size.
        SilverkiteColumn.COLS_TREND_DAY_OF_WEEK: "auto",
        # Omitted key is treated the same as "auto".
        # SilverkiteColumn.COLS_TREND_WEEKLY_SEAS: "auto"
    },
    # Allows up to fourier order 2 for weekly seasonality interactions
    max_weekly_seas_interaction_order=2
)

# Turns on a few feature sets relevant for hourly data
custom = dict(
    feature_sets_enabled={
        SilverkiteColumn.COLS_HOUR_OF_WEEK: False,
        SilverkiteColumn.COLS_WEEKEND_SEAS: True,
        SilverkiteColumn.COLS_DAY_OF_WEEK_SEAS: True,
        SilverkiteColumn.COLS_TREND_DAILY_SEAS: True,
        SilverkiteColumn.COLS_EVENT_SEAS: False,  # unnecessary when COLS_EVENT_WEEKEND_SEAS is used
        SilverkiteColumn.COLS_EVENT_WEEKEND_SEAS: True,
        SilverkiteColumn.COLS_DAY_OF_WEEK: False,
        SilverkiteColumn.COLS_TREND_WEEKEND: True,
        SilverkiteColumn.COLS_TREND_DAY_OF_WEEK: True,
        SilverkiteColumn.COLS_TREND_WEEKLY_SEAS: True
    },
    # Allows up to fourier order 2 for daily/weekly seasonality interactions
    max_daily_seas_interaction_order=2,
    max_weekly_seas_interaction_order=2
)

To check which features sets are enabled by default for your dataset, call get_feature_sets_enabled.

• The parameter num_days is the number of days in your input timeseries (historical data for training, without future dates for regressors). It does not need to be exact.

from greykite.algo.forecast.silverkite.forecast_simple_silverkite import SimpleSilverkiteForecast
from greykite.common.enums import SimpleTimeFrequencyEnum

silverkite = SimpleSilverkiteForecast()
# 60 days of hourly data
silverkite._SimpleSilverkiteForecast__get_feature_sets_enabled(
    simple_freq=SimpleTimeFrequencyEnum.HOUR.name,
    num_days=60,
    feature_sets_enabled="auto")
# 60 days of daily data
silverkite._SimpleSilverkiteForecast__get_feature_sets_enabled(
    simple_freq=SimpleTimeFrequencyEnum.DAY.name,
    num_days=60,
    feature_sets_enabled="auto")
# 30 weeks of weekly data
silverkite._SimpleSilverkiteForecast__get_feature_sets_enabled(
    simple_freq=SimpleTimeFrequencyEnum.WEEK.name,
    num_days=7*30,
    feature_sets_enabled="auto")
# 30 months of monthly data
silverkite._SimpleSilverkiteForecast__get_feature_sets_enabled(
    simple_freq=SimpleTimeFrequencyEnum.MONTH.name,
    num_days=30*30,
    feature_sets_enabled="auto")
# 20 quarters of quarterly data
silverkite._SimpleSilverkiteForecast__get_feature_sets_enabled(
    simple_freq=SimpleTimeFrequencyEnum.QUARTER.name,
    num_days=90*20,
    feature_sets_enabled="auto")
# 12 years of yearly data
silverkite._SimpleSilverkiteForecast__get_feature_sets_enabled(
    simple_freq=SimpleTimeFrequencyEnum.YEAR.name,
    num_days=365*12,
    feature_sets_enabled="auto")

Specify model terms

For even finer control than feature_sets_enabled, you can specify additional model terms via extra_pred_cols. Any valid patsy model formula term is accepted. You need to know how columns are internally coded to use this function. Most users will not need this option.

Note

While it’s possible to add many terms in the model, a high degree of complexity may not generalize well into the forecast period and should not be necessary for most forecasts.

extra_pred_cols : `list` [`str`] or None or a list of such values for grid search, default None
    Names of extra predictor columns to pass to ``forecast_silverkite``.
    The standard interactions can be controlled via ``feature_sets_enabled`` parameter.
    Accepts any valid patsy model formula term. Can be used to model complex interactions
    of time features, events, seasonality, changepoints, regressors. Columns should be
    generated by ``build_silverkite_features`` or included with input data.
    These are added to any features already included by ``feature_sets_enabled`` and
    terms specified by ``model``.

Example:

import greykite.common.constants as cst
from greykite.framework.utils.result_summary import patsy_categorical_term

# Provides all holidays of interest
holiday_names = ["Christmas Day", "Thanksgiving", "Labor Day"]

# Adds day-of-holiday interaction with is_weekend
# (does not add the interaction on days offset from the holiday)
extra_pred_cols = []
event_levels = [cst.EVENT_DEFAULT, cst.EVENT_INDICATOR]
for holiday_name in holiday_names:
    holiday_term = patsy_categorical_term(
        term=f"{cst.EVENT_PREFIX}_{holiday_name}",  # holiday column name
        levels=event_levels)  # levels for holiday categorical variable
    extra_pred_cols += [f"is_weekend:{holiday_term}"]

# Tells the model to include these parameters
custom = dict(extra_pred_cols=extra_pred_cols)

Note

Contact us if you’re using extra_pred_cols. If your model terms are useful for others, we can add them to feature_sets_enabled.

Similarly, you may specify terms to exclude via "drop_pred_cols":

drop_pred_cols : `list` [`str`] or None, default None
    Names of predictor columns to be dropped from the final model.
    Ignored if None.

To directly specify all the terms used in the final model, use "explicit_pred_cols":

explicit_pred_cols : `list` [`str`] or None, default None
    Names of the explicit predictor columns which will be
    the only variables in the final model. Note that this overwrites
    the generated predictors in the model and may include new
    terms not appearing in the predictors (e.g. interaction terms).
    Ignored if None.

Forecast limits

You may prevent the forecast from going above or below pre-set values via min_admissible_value and max_admissible_value.

This can be useful, for example, if you are forecasting a non-negative metric.

min_admissible_value : `float` or `double` or `int` or None, default None
    The lowest admissible value for the forecasts and prediction
    intervals. Any value below this will be mapped back to this value.
    If None, there is no lower bound.
max_admissible_value : `float` or `double` or `int`, default None
    The highest admissible value for the forecasts and prediction
    intervals. Any value above this will be mapped back to this value.
    If None, there is no upper bound.

Examples:

# enforce non-negative forecast
custom = dict(
    min_admissible_value=0
)

# specifies an acceptable range
custom = dict(
    min_admissible_value=1e3
    max_admissible_value=1e6
)

Normalization

It can be helpful to normalize features, especially when features have different magnitudes and regularization is used.

normalize_method : `str` or None, default None
    The normalization method for the feature matrix.
    Available values are "statistical" and "min_max".

Examples:

custom = dict(
    normalize_method="statistical"
)
custom = dict(
    normalize_method="min_max"
)

The statistical method removes the “mean” and divides by “std” for each column. The min_max method removes the “min” and divides by the “max - min” for each column. For details, see normalize_df.