MLForecast

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Data

This shows an example with just 4 series of the M4 dataset. If you want to run it yourself on all of them, you can refer to this notebook.

import random
import tempfile

import lightgbm as lgb
import matplotlib.pyplot as plt
import numpy as np
import xgboost as xgb
from sklearn.linear_model import LinearRegression
from utilsforecast.feature_engineering import time_features
from utilsforecast.plotting import plot_series

from mlforecast.lag_transforms import ExpandingMean, ExponentiallyWeightedMean, RollingMean
from mlforecast.lgb_cv import LightGBMCV
from mlforecast.target_transforms import Differences, LocalStandardScaler
from mlforecast.utils import generate_daily_series

df = pd.read_parquet('https://datasets-nixtla.s3.amazonaws.com/m4-hourly.parquet')
ids = df['unique_id'].unique()
random.seed(0)
sample_ids = random.choices(ids, k=4)
sample_df = df[df['unique_id'].isin(sample_ids)]
sample_df

We now split this data into train and validation.

horizon = 48
valid = sample_df.groupby('unique_id').tail(horizon)
train = sample_df.drop(valid.index)
train.shape, valid.shape

((3840, 3), (192, 3))

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MLForecast

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 MLForecast (models:Union[sklearn.base.BaseEstimator,List[sklearn.base.Bas
             eEstimator],Dict[str,sklearn.base.BaseEstimator]],
             freq:Union[int,str], lags:Optional[Iterable[int]]=None, lag_t
             ransforms:Optional[Dict[int,List[Union[Callable,Tuple[Callabl
             e,Any]]]]]=None,
             date_features:Optional[Iterable[Union[str,Callable]]]=None,
             num_threads:int=1, target_transforms:Optional[List[Union[mlfo
             recast.target_transforms.BaseTargetTransform,mlforecast.targe
             t_transforms._BaseGroupedArrayTargetTransform]]]=None,
             lag_transforms_namer:Optional[Callable]=None)

Forecasting pipeline

The MLForecast object encapsulates the feature engineering + training the models + forecasting

fcst = MLForecast(
    models=lgb.LGBMRegressor(random_state=0, verbosity=-1),
    freq=1,
    lags=[24 * (i+1) for i in range(7)],
    lag_transforms={
        48: [ExponentiallyWeightedMean(alpha=0.3)],
    },
    num_threads=1,
    target_transforms=[Differences([24])],
)
fcst

MLForecast(models=[LGBMRegressor], freq=1, lag_features=['lag24', 'lag48', 'lag72', 'lag96', 'lag120', 'lag144', 'lag168', 'exponentially_weighted_mean_lag48_alpha0.3'], date_features=[], num_threads=1)

Once we have this setup we can compute the features and fit the model.

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MLForecast.fit

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 MLForecast.fit
                 (df:Union[pandas.core.frame.DataFrame,polars.dataframe.fr
                 ame.DataFrame], id_col:str='unique_id',
                 time_col:str='ds', target_col:str='y',
                 static_features:Optional[List[str]]=None,
                 dropna:bool=True, keep_last_n:Optional[int]=None,
                 max_horizon:Optional[int]=None, prediction_intervals:Opti
                 onal[mlforecast.utils.PredictionIntervals]=None,
                 fitted:bool=False, as_numpy:bool=False,
                 weight_col:Optional[str]=None)

Apply the feature engineering and train the models.

fcst = MLForecast(
    models=lgb.LGBMRegressor(random_state=0, verbosity=-1),
    freq=1,
    lags=[24 * (i+1) for i in range(7)],
    lag_transforms={
        48: [ExponentiallyWeightedMean(alpha=0.3)],
    },
    num_threads=1,
    target_transforms=[Differences([24])],
)

train2 = train.copy()
train2['weight'] = np.random.default_rng(seed=0).random(train2.shape[0])
fcst.fit(train2, weight_col='weight', as_numpy=True).predict(5)

fcst.cross_validation(train2, n_windows=2, h=5, weight_col='weight', as_numpy=True)

fcst.fit(train, fitted=True);

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MLForecast.save

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 MLForecast.save (path:Union[str,pathlib.Path])

Save forecast object

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MLForecast.load

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 MLForecast.load (path:Union[str,pathlib.Path])

Load forecast object

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MLForecast.update

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 MLForecast.update
                    (df:Union[pandas.core.frame.DataFrame,polars.dataframe
                    .frame.DataFrame])

Update the values of the stored series.

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MLForecast.make_future_dataframe

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 MLForecast.make_future_dataframe (h:int)

Create a dataframe with all ids and future times in the forecasting horizon.

expected_future = fcst.make_future_dataframe(h=1)
expected_future

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MLForecast.get_missing_future

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 MLForecast.get_missing_future (h:int, X_df:~DFType)

Get the missing id and time combinations in X_df.

missing_future = fcst.get_missing_future(h=1, X_df=expected_future.head(2))
pd.testing.assert_frame_equal(
    missing_future,
    expected_future.tail(2).reset_index(drop=True)
)

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MLForecast.forecast_fitted_values

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 MLForecast.forecast_fitted_values
                                    (level:Optional[List[Union[int,float]]
                                    ]=None)

Access in-sample predictions.

fcst.forecast_fitted_values()

fcst.forecast_fitted_values(level=[90])

Once we’ve run this we’re ready to compute our predictions.

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MLForecast.predict

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 MLForecast.predict (h:int,
                     before_predict_callback:Optional[Callable]=None,
                     after_predict_callback:Optional[Callable]=None,
                     new_df:Optional[~DFType]=None,
                     level:Optional[List[Union[int,float]]]=None,
                     X_df:Optional[~DFType]=None,
                     ids:Optional[List[str]]=None)

Compute the predictions for the next h steps.

predictions = fcst.predict(horizon)

We can see at a couple of results.

results = valid.merge(predictions, on=['unique_id', 'ds'])
fig = plot_series(forecasts_df=results)

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Prediction intervals

With MLForecast, you can generate prediction intervals using Conformal Prediction. To configure Conformal Prediction, you need to pass an instance of the PredictionIntervals class to the prediction_intervals argument of the fit method. The class takes three parameters: n_windows, h and method.

• n_windows represents the number of cross-validation windows used to calibrate the intervals
• h is the forecast horizon
• method can be conformal_distribution or conformal_error; conformal_distribution (default) creates forecasts paths based on the cross-validation errors and calculate quantiles using those paths, on the other hand conformal_error calculates the error quantiles to produce prediction intervals. The strategy will adjust the intervals for each horizon step, resulting in different widths for each step. Please note that a minimum of 2 cross-validation windows must be used.

fcst.fit(
    train,
    prediction_intervals=PredictionIntervals(n_windows=3, h=48)
);

After that, you just have to include your desired confidence levels to the predict method using the level argument. Levels must lie between 0 and 100.

predictions_w_intervals = fcst.predict(48, level=[50, 80, 95])
predictions_w_intervals.head()

Let’s explore the generated intervals.

results = valid.merge(predictions_w_intervals, on=['unique_id', 'ds'])
fig = plot_series(forecasts_df=results, level=[50, 80, 95])

If you want to reduce the computational time and produce intervals with the same width for the whole forecast horizon, simple pass h=1 to the PredictionIntervals class. The caveat of this strategy is that in some cases, variance of the absolute residuals maybe be small (even zero), so the intervals may be too narrow.

fcst.fit(
    train,  
    prediction_intervals=PredictionIntervals(n_windows=3, h=1)
);

predictions_w_intervals_ws_1 = fcst.predict(48, level=[80, 90, 95])

Let’s explore the generated intervals.

results = valid.merge(predictions_w_intervals_ws_1, on=['unique_id', 'ds'])
fig = plot_series(forecasts_df=results, level=[90])

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Forecast using a pretrained model

MLForecast allows you to use a pretrained model to generate forecasts for a new dataset. Simply provide a pandas dataframe containing the new observations as the value for the new_df argument when calling the predict method. The dataframe should have the same structure as the one used to fit the model, including any features and time series data. The function will then use the pretrained model to generate forecasts for the new observations. This allows you to easily apply a pretrained model to a new dataset and generate forecasts without the need to retrain the model.

ercot_df = pd.read_csv('https://datasets-nixtla.s3.amazonaws.com/ERCOT-clean.csv')
# we have to convert the ds column to integers
# since MLForecast was trained with that structure
ercot_df['ds'] = np.arange(1, len(ercot_df) + 1)
# use the `new_df` argument to pass the ercot dataset 
ercot_fcsts = fcst.predict(horizon, new_df=ercot_df)
fig = plot_series(ercot_df, ercot_fcsts, max_insample_length=48 * 2)

If you want to take a look at the data that will be used to train the models you can call Forecast.preprocess.

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MLForecast.preprocess

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 MLForecast.preprocess (df:~DFType, id_col:str='unique_id',
                        time_col:str='ds', target_col:str='y',
                        static_features:Optional[List[str]]=None,
                        dropna:bool=True, keep_last_n:Optional[int]=None,
                        max_horizon:Optional[int]=None,
                        return_X_y:bool=False, as_numpy:bool=False,
                        weight_col:Optional[str]=None)

Add the features to data.

prep_df = fcst.preprocess(train)
prep_df

If we do this we then have to call Forecast.fit_models, since this only stores the series information.

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MLForecast.fit_models

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 MLForecast.fit_models (X:Union[pandas.core.frame.DataFrame,polars.datafra
                        me.frame.DataFrame,numpy.ndarray],
                        y:numpy.ndarray)

Manually train models. Use this if you called MLForecast.preprocess beforehand.

X, y = prep_df.drop(columns=['unique_id', 'ds', 'y']), prep_df['y']
fcst.fit_models(X, y)

MLForecast(models=[LGBMRegressor], freq=1, lag_features=['lag24', 'lag48', 'lag72', 'lag96', 'lag120', 'lag144', 'lag168', 'exponentially_weighted_mean_lag48_alpha0.3'], date_features=[], num_threads=1)

predictions2 = fcst.predict(horizon)
pd.testing.assert_frame_equal(predictions, predictions2)

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MLForecast.cross_validation

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 MLForecast.cross_validation (df:~DFType, n_windows:int, h:int,
                              id_col:str='unique_id', time_col:str='ds',
                              target_col:str='y',
                              step_size:Optional[int]=None,
                              static_features:Optional[List[str]]=None,
                              dropna:bool=True,
                              keep_last_n:Optional[int]=None,
                              refit:Union[bool,int]=True,
                              max_horizon:Optional[int]=None, before_predi
                              ct_callback:Optional[Callable]=None, after_p
                              redict_callback:Optional[Callable]=None, pre
                              diction_intervals:Optional[mlforecast.utils.
                              PredictionIntervals]=None,
                              level:Optional[List[Union[int,float]]]=None,
                              input_size:Optional[int]=None,
                              fitted:bool=False, as_numpy:bool=False,
                              weight_col:Optional[str]=None)

Perform time series cross validation. Creates n_windows splits where each window has h test periods, trains the models, computes the predictions and merges the actuals.

If we would like to know how good our forecast will be for a specific model and set of features then we can perform cross validation. What cross validation does is take our data and split it in two parts, where the first part is used for training and the second one for validation. Since the data is time dependant we usually take the last x observations from our data as the validation set.

This process is implemented in MLForecast.cross_validation, which takes our data and performs the process described above for n_windows times where each window has h validation samples in it. For example, if we have 100 samples and we want to perform 2 backtests each of size 14, the splits will be as follows:

1. Train: 1 to 72. Validation: 73 to 86.
2. Train: 1 to 86. Validation: 87 to 100.

You can control the size between each cross validation window using the step_size argument. For example, if we have 100 samples and we want to perform 2 backtests each of size 14 and move one step ahead in each fold (step_size=1), the splits will be as follows:

1. Train: 1 to 85. Validation: 86 to 99.
2. Train: 1 to 86. Validation: 87 to 100.

You can also perform cross validation without refitting your models for each window by setting refit=False. This allows you to evaluate the performance of your models using multiple window sizes without having to retrain them each time.

fcst = MLForecast(
    models=lgb.LGBMRegressor(random_state=0, verbosity=-1),
    freq=1,
    lags=[24 * (i+1) for i in range(7)],
    lag_transforms={
        1: [RollingMean(window_size=24)],
        24: [RollingMean(window_size=24)],
        48: [ExponentiallyWeightedMean(alpha=0.3)],
    },
    num_threads=1,
    target_transforms=[Differences([24])],
)
cv_results = fcst.cross_validation(
    train,
    n_windows=2,
    h=horizon,
    step_size=horizon,
    fitted=True,
)
cv_results

Since we set fitted=True we can access the predictions for the training sets as well with the cross_validation_fitted_values method.

fcst.cross_validation_fitted_values()

We can also compute prediction intervals by passing a configuration to prediction_intervals as well as values for the width through levels.

cv_results_intervals = fcst.cross_validation(
    train,
    n_windows=2,
    h=horizon,
    step_size=horizon,
    prediction_intervals=PredictionIntervals(h=horizon),
    level=[80, 90]
)
cv_results_intervals

The refit argument allows us to control if we want to retrain the models in every window. It can either be:

• A boolean: True will retrain on every window and False only on the first one.
• A positive integer: The models will be trained on the first window and then every refit windows.

fcst = MLForecast(
    models=LinearRegression(),
    freq=1,
    lags=[1, 24],
)
for refit, expected_models in zip([True, False, 2], [4, 1, 2]):
    fcst.cross_validation(
        train,
        n_windows=4,
        h=horizon,
        refit=refit,
    )
    test_eq(len(fcst.cv_models_), expected_models)

fig = plot_series(forecasts_df=cv_results.drop(columns='cutoff'))

fig = plot_series(forecasts_df=cv_results_intervals.drop(columns='cutoff'), level=[90])

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MLForecast.from_cv

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 MLForecast.from_cv (cv:mlforecast.lgb_cv.LightGBMCV)

Once you’ve found a set of features and parameters that work for your problem you can build a forecast object from it using MLForecast.from_cv, which takes the trained LightGBMCV object and builds an MLForecast object that will use the same features and parameters. Then you can call fit and predict as you normally would.

cv = LightGBMCV(
    freq=1,
    lags=[24 * (i+1) for i in range(7)],
    lag_transforms={
        48: [ExponentiallyWeightedMean(alpha=0.3)],
    },
    num_threads=1,
    target_transforms=[Differences([24])]
)
hist = cv.fit(
    train,
    n_windows=2,
    h=horizon,
    params={'verbosity': -1},
)

[10] mape: 0.118569
[20] mape: 0.111506
[30] mape: 0.107314
[40] mape: 0.106089
[50] mape: 0.106630
Early stopping at round 50
Using best iteration: 40

fcst = MLForecast.from_cv(cv)
assert cv.best_iteration_ == fcst.models['LGBMRegressor'].n_estimators