PERMBU

In many cases, only the time series at the lowest level of the hierarchies (bottom time series) are available. HierarchicalForecast has tools to create time series for all hierarchies and also allows you to calculate prediction intervals for all hierarchies. In this notebook we will see how to do it.

!pip install hierarchicalforecast statsforecast

import pandas as pd

# compute base forecast no coherent
from statsforecast.models import AutoARIMA
from statsforecast.core import StatsForecast

#obtain hierarchical reconciliation methods and evaluation
from hierarchicalforecast.methods import BottomUp, MinTrace
from hierarchicalforecast.utils import aggregate, HierarchicalPlot
from hierarchicalforecast.core import HierarchicalReconciliation

Aggregate bottom time series

In this example we will use the Tourism dataset from the Forecasting: Principles and Practice book. The dataset only contains the time series at the lowest level, so we need to create the time series for all hierarchies.

Y_df = pd.read_csv('https://raw.githubusercontent.com/Nixtla/transfer-learning-time-series/main/datasets/tourism.csv')
Y_df = Y_df.rename({'Trips': 'y', 'Quarter': 'ds'}, axis=1)
Y_df.insert(0, 'Country', 'Australia')
Y_df = Y_df[['Country', 'Region', 'State', 'Purpose', 'ds', 'y']]
Y_df['ds'] = Y_df['ds'].str.replace(r'(\d+) (Q\d)', r'\1-\2', regex=True)
Y_df['ds'] = pd.PeriodIndex(Y_df["ds"], freq='Q').to_timestamp()
Y_df.head()

	Country	Region	State	Purpose	ds	y
0	Australia	Adelaide	South Australia	Business	1998-01-01	135.077690
1	Australia	Adelaide	South Australia	Business	1998-04-01	109.987316
2	Australia	Adelaide	South Australia	Business	1998-07-01	166.034687
3	Australia	Adelaide	South Australia	Business	1998-10-01	127.160464
4	Australia	Adelaide	South Australia	Business	1999-01-01	137.448533

The dataset can be grouped in the following strictly hierarchical structure.

spec = [
    ['Country'],
    ['Country', 'State'], 
    ['Country', 'State', 'Region']
]

Using the aggregate function from HierarchicalForecast we can get the full set of time series.

Y_df, S_df, tags = aggregate(df=Y_df, spec=spec)

Y_df.head()

	unique_id	ds	y
0	Australia	1998-01-01	23182.197269
1	Australia	1998-04-01	20323.380067
2	Australia	1998-07-01	19826.640511
3	Australia	1998-10-01	20830.129891
4	Australia	1999-01-01	22087.353380

S_df.iloc[:5, :5]

	unique_id	Australia/ACT/Canberra	Australia/New South Wales/Blue Mountains	Australia/New South Wales/Capital Country	Australia/New South Wales/Central Coast
0	Australia	1.0	1.0	1.0	1.0
1	Australia/ACT	1.0	0.0	0.0	0.0
2	Australia/New South Wales	0.0	1.0	1.0	1.0
3	Australia/Northern Territory	0.0	0.0	0.0	0.0
4	Australia/Queensland	0.0	0.0	0.0	0.0

tags['Country/State']

array(['Australia/ACT', 'Australia/New South Wales',
       'Australia/Northern Territory', 'Australia/Queensland',
       'Australia/South Australia', 'Australia/Tasmania',
       'Australia/Victoria', 'Australia/Western Australia'], dtype=object)

We can visualize the S matrix and the data using the HierarchicalPlot class as follows.

hplot = HierarchicalPlot(S=S_df, tags=tags)

hplot.plot_summing_matrix()

hplot.plot_hierarchically_linked_series(
    bottom_series='Australia/ACT/Canberra',
    Y_df=Y_df
)

Split Train/Test sets

We use the final two years (8 quarters) as test set.

Y_test_df = Y_df.groupby('unique_id', as_index=False).tail(8)
Y_train_df = Y_df.drop(Y_test_df.index)

Y_train_df.groupby('unique_id').size()

unique_id
Australia                                                 72
Australia/ACT                                             72
Australia/ACT/Canberra                                    72
Australia/New South Wales                                 72
Australia/New South Wales/Blue Mountains                  72
                                                          ..
Australia/Western Australia/Australia's Coral Coast       72
Australia/Western Australia/Australia's Golden Outback    72
Australia/Western Australia/Australia's North West        72
Australia/Western Australia/Australia's South West        72
Australia/Western Australia/Experience Perth              72
Length: 85, dtype: int64

Computing base forecasts

The following cell computes the base forecasts for each time series in Y_df using the AutoARIMA and model. Observe that Y_hat_df contains the forecasts but they are not coherent. To reconcile the prediction intervals we need to calculate the uncoherent intervals using the level argument of StatsForecast.

fcst = StatsForecast(models=[AutoARIMA(season_length=4)], 
                     freq='QS', n_jobs=-1)
Y_hat_df = fcst.forecast(df=Y_train_df, h=8, fitted=True, level=[80, 90])
Y_fitted_df = fcst.forecast_fitted_values()

Reconcile forecasts and compute prediction intervals using PERMBU

The following cell makes the previous forecasts coherent using the HierarchicalReconciliation class. In this example we use BottomUp and MinTrace. If you want to calculate prediction intervals, you have to use the level argument as follows and also intervals_method='permbu'.

reconcilers = [
    BottomUp(),
    MinTrace(method='mint_shrink'),
    MinTrace(method='ols')
]
hrec = HierarchicalReconciliation(reconcilers=reconcilers)
Y_rec_df = hrec.reconcile(Y_hat_df=Y_hat_df, Y_df=Y_fitted_df,
                          S_df=S_df, tags=tags,
                          level=[80, 90], intervals_method='permbu')

The dataframe Y_rec_df contains the reconciled forecasts.

Y_rec_df.head()

	unique_id	ds	AutoARIMA	AutoARIMA-lo-90	AutoARIMA-lo-80	AutoARIMA-hi-80	AutoARIMA-hi-90	AutoARIMA/BottomUp	AutoARIMA/BottomUp-lo-90	AutoARIMA/BottomUp-lo-80	…	AutoARIMA/MinTrace_method-mint_shrink	AutoARIMA/MinTrace_method-mint_shrink-lo-90	AutoARIMA/MinTrace_method-mint_shrink-lo-80	AutoARIMA/MinTrace_method-mint_shrink-hi-80	AutoARIMA/MinTrace_method-mint_shrink-hi-90	AutoARIMA/MinTrace_method-ols	AutoARIMA/MinTrace_method-ols-lo-90	AutoARIMA/MinTrace_method-ols-lo-80	AutoARIMA/MinTrace_method-ols-hi-80	AutoARIMA/MinTrace_method-ols-hi-90
0	Australia	2016-01-01	26212.553553	24705.948180	25038.715077	27386.392029	27719.158927	24955.501571	24143.056131	24387.230200	…	25413.657606	24705.682710	24905.677772	25928.334367	26050.232961	26142.818016	25525.081721	25656.537995	26606.345032	26832.423921
1	Australia	2016-04-01	25033.667125	23337.267588	23711.954696	26355.379554	26730.066662	23421.312868	22762.045247	22904.087197	…	24058.906411	23486.828548	23627.152623	24659.405484	24847.778503	24946.338649	24297.061230	24434.805048	25535.549040	25640.659918
2	Australia	2016-07-01	24507.027198	22640.028798	23052.396413	25961.657983	26374.025599	22807.706826	22065.402373	22223.120404	…	23438.863893	22672.658701	22888.299153	23971.724733	24179.548677	24407.245003	23712.841797	23834.054327	25027.073615	25189.869286
3	Australia	2016-10-01	25598.928613	23575.665243	24022.547410	27175.309816	27622.191983	23471.845870	22677.593575	22892.328939	…	24322.049398	23619.419712	23682.803746	24847.299228	25028.345572	25496.855604	24740.210465	24923.560783	26094.250414	26273.617732
4	Australia	2017-01-01	26982.576796	24669.535238	25180.421285	28784.732308	29295.618354	24668.735931	23760.842072	23964.283124	…	25520.163549	24720.304392	24910.106650	26170.552678	26347.181903	26853.231907	26045.213677	26149.753374	27502.499674	27733.985566

Plot forecasts

Then we can plot the probabilist forecasts using the following function.

plot_df = Y_df.merge(Y_rec_df, on=['unique_id', 'ds'], how="outer")

Plot single time series

hplot.plot_series(
    series='Australia',
    Y_df=plot_df, 
    models=['y', 'AutoARIMA', 
            'AutoARIMA/MinTrace_method-ols',
            'AutoARIMA/BottomUp'
           ],
    level=[80]
)

Plot hierarchichally linked time series

hplot.plot_hierarchically_linked_series(
    bottom_series='Australia/Western Australia/Experience Perth',
    Y_df=plot_df, 
    models=['y', 'AutoARIMA', 'AutoARIMA/MinTrace_method-ols', 'AutoARIMA/BottomUp'],
    level=[80]
)

# ACT only has Canberra
hplot.plot_hierarchically_linked_series(
    bottom_series='Australia/ACT/Canberra',
    Y_df=plot_df, 
    models=['y', 'AutoARIMA/MinTrace_method-mint_shrink'],
    level=[80, 90]
)

Getting Started

Tutorials

API Reference

Aggregate bottom time series

Split Train/Test sets

Computing base forecasts

Reconcile forecasts and compute prediction intervals using PERMBU

Plot forecasts

Plot single time series

Plot hierarchichally linked time series

References

​Aggregate bottom time series

​Split Train/Test sets

​Computing base forecasts

​Reconcile forecasts and compute prediction intervals using PERMBU

​Plot forecasts

​Plot single time series

​Plot hierarchichally linked time series

​References

Aggregate bottom time series

Split Train/Test sets

Computing base forecasts

Reconcile forecasts and compute prediction intervals using PERMBU

Plot forecasts

Plot single time series

Plot hierarchichally linked time series

References