Independent multi-series forecasting¶
In univariate time series forecasting, a single time series is modeled as a linear or nonlinear combination of its lags, where past values of the series are used to forecast its future. In multi-series forecasting, two or more time series are modeled together using a single model.
In independent multi-series forecasting a single model is trained for all time series, but each time series remains independent of the others, meaning that past values of one series are not used as predictors of other series. However, modeling them together is useful because the series may follow the same intrinsic pattern regarding their past and future values. For instance, the sales of products A and B in the same store may not be related, but they follow the same dynamics, that of the store.
To predict the next n steps, the strategy of recursive multi-step forecasting is applied, with the only difference being that the series name for which to estimate the predictions needs to be indicated.
Using the ForecasterAutoregMultiSeries
and ForecasterAutoregMultiSeriesCustom
classes, it is possible to easily build machine learning models for independent multi-series forecasting.
  Note
See ForecasterAutoregMultiVariate for dependent multi-series forecasting (multivariate time series).
Libraries¶
# Libraries
# ==============================================================================
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
from sklearn.preprocessing import StandardScaler
from sklearn.linear_model import Ridge
from sklearn.metrics import mean_absolute_error
from skforecast.ForecasterAutoregMultiSeries import ForecasterAutoregMultiSeries
from skforecast.model_selection_multiseries import backtesting_forecaster_multiseries
from skforecast.model_selection_multiseries import grid_search_forecaster_multiseries
Data¶
# Data download
# ==============================================================================
url = (
'https://raw.githubusercontent.com/JoaquinAmatRodrigo/skforecast/master/'
'data/simulated_items_sales.csv'
)
data = pd.read_csv(url, sep=',')
# Data preparation
# ==============================================================================
data['date'] = pd.to_datetime(data['date'], format='%Y-%m-%d')
data = data.set_index('date')
data = data.asfreq('D')
data = data.sort_index()
data.head()
item_1 | item_2 | item_3 | |
---|---|---|---|
date | |||
2012-01-01 | 8.253175 | 21.047727 | 19.429739 |
2012-01-02 | 22.777826 | 26.578125 | 28.009863 |
2012-01-03 | 27.549099 | 31.751042 | 32.078922 |
2012-01-04 | 25.895533 | 24.567708 | 27.252276 |
2012-01-05 | 21.379238 | 18.191667 | 20.357737 |
# Split data into train-val-test
# ==============================================================================
end_train = '2014-07-15 23:59:00'
data_train = data.loc[:end_train, :].copy()
data_test = data.loc[end_train:, :].copy()
print(
f"Train dates : {data_train.index.min()} --- {data_train.index.max()} "
f"(n={len(data_train)})"
)
print(
f"Test dates : {data_test.index.min()} --- {data_test.index.max()} "
f"(n={len(data_test)})"
)
Train dates : 2012-01-01 00:00:00 --- 2014-07-15 00:00:00 (n=927) Test dates : 2014-07-16 00:00:00 --- 2015-01-01 00:00:00 (n=170)
# Plot time series
# ==============================================================================
fig, axes = plt.subplots(nrows=3, ncols=1, figsize=(9, 5), sharex=True)
data_train['item_1'].plot(label='train', ax=axes[0])
data_test['item_1'].plot(label='test', ax=axes[0])
axes[0].set_xlabel('')
axes[0].set_ylabel('sales')
axes[0].set_title('Item 1')
axes[0].legend()
data_train['item_2'].plot(label='train', ax=axes[1])
data_test['item_2'].plot(label='test', ax=axes[1])
axes[1].set_xlabel('')
axes[1].set_ylabel('sales')
axes[1].set_title('Item 2')
data_train['item_3'].plot(label='train', ax=axes[2])
data_test['item_3'].plot(label='test', ax=axes[2])
axes[2].set_xlabel('')
axes[2].set_ylabel('sales')
axes[2].set_title('Item 3')
fig.tight_layout()
plt.show();
Train and predict ForecasterAutoregMultiSeries¶
# Create and fit forecaster multi series
# ==============================================================================
forecaster = ForecasterAutoregMultiSeries(
regressor = Ridge(random_state=123),
lags = 24,
transformer_series = None,
transformer_exog = None,
weight_func = None,
series_weights = None
)
forecaster.fit(series=data_train)
forecaster
============================ ForecasterAutoregMultiSeries ============================ Regressor: Ridge(random_state=123) Lags: [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24] Transformer for series: None Transformer for exog: None Window size: 24 Series levels (names): ['item_1', 'item_2', 'item_3'] Series weights: None Weight function included: False Exogenous included: False Type of exogenous variable: None Exogenous variables names: None Training range: [Timestamp('2012-01-01 00:00:00'), Timestamp('2014-07-15 00:00:00')] Training index type: DatetimeIndex Training index frequency: D Regressor parameters: {'alpha': 1.0, 'copy_X': True, 'fit_intercept': True, 'max_iter': None, 'positive': False, 'random_state': 123, 'solver': 'auto', 'tol': 0.0001} fit_kwargs: {} Creation date: 2023-05-29 13:15:11 Last fit date: 2023-05-29 13:15:11 Skforecast version: 0.8.1 Python version: 3.10.11 Forecaster id: None
Two methods can be use to predict the next n steps: predict()
or predict_interval()
. The argument levels
is used to indicate for which series estimate predictions. If None
all series will be predicted.
# Predict and predict_interval
# ==============================================================================
steps = 24
# Predictions for item_1
predictions_item_1 = forecaster.predict(steps=steps, levels='item_1')
display(predictions_item_1.head(3))
# Interval predictions for item_1 and item_2
predictions_intervals = forecaster.predict_interval(steps=steps, levels=['item_1', 'item_2'])
display(predictions_intervals.head(3))
item_1 | |
---|---|
2014-07-16 | 25.497376 |
2014-07-17 | 24.866972 |
2014-07-18 | 24.281173 |
item_1 | item_1_lower_bound | item_1_upper_bound | item_2 | item_2_lower_bound | item_2_upper_bound | |
---|---|---|---|---|---|---|
2014-07-16 | 25.497376 | 23.220087 | 28.226068 | 10.694506 | 7.093046 | 15.518896 |
2014-07-17 | 24.866972 | 22.141168 | 27.389805 | 11.080091 | 6.467676 | 16.534679 |
2014-07-18 | 24.281173 | 21.688393 | 26.981395 | 11.490882 | 7.077863 | 16.762530 |
Backtesting Multi Series¶
As in the predict
method, the levels
at which backtesting is performed must be indicated. The argument can also be set to None
to perform backtesting at all levels.
# Backtesting Multi Series
# ==============================================================================
metrics_levels, backtest_predictions = backtesting_forecaster_multiseries(
forecaster = forecaster,
series = data,
levels = None,
steps = 24,
metric = 'mean_absolute_error',
initial_train_size = len(data_train),
fixed_train_size = True,
gap = 0,
allow_incomplete_fold = True,
refit = True,
verbose = False,
show_progress = True
)
print("Backtest metrics")
display(metrics_levels)
print("")
print("Backtest predictions")
backtest_predictions.head(4)
0%| | 0/8 [00:00<?, ?it/s]
Backtest metrics
levels | mean_absolute_error | |
---|---|---|
0 | item_1 | 1.360675 |
1 | item_2 | 2.332392 |
2 | item_3 | 3.155592 |
Backtest predictions
item_1 | item_2 | item_3 | |
---|---|---|---|
2014-07-16 | 25.497376 | 10.694506 | 11.275026 |
2014-07-17 | 24.866972 | 11.080091 | 11.313510 |
2014-07-18 | 24.281173 | 11.490882 | 13.030112 |
2014-07-19 | 23.515499 | 11.548922 | 13.378282 |
Hyperparameter tuning and lags selection Multi Series¶
Functions grid_search_forecaster_multiseries
and random_search_forecaster_multiseries
in the module model_selection_multiseries
allow for lag and hyperparameter optimization. The optimization is performed in the same way as in the other forecasters, see the user guide here, except for the levels
argument:
levels
: level(s) at which the forecaster is optimized, for example:If
levels = ['item_1', 'item_2', 'item_3']
(Same aslevels = None
), the function will search for the lags and hyperparameters that minimize the average error of the predictions of all the time series. The resulting metric will be the average of all levels.If
levels = 'item_1'
(Same aslevels = ['item_1']
), the function will search for the lags and hyperparameters that minimize the error of theitem_1
predictions. The resulting metric will be the one calculated foritem_1
.
The following example shows how to use grid_search_forecaster_multiseries
to find the best lags and model hyperparameters for all time series:
# Create Forecaster multi series
# ==============================================================================
forecaster = ForecasterAutoregMultiSeries(
regressor = Ridge(random_state=123),
lags = 24,
transformer_series = StandardScaler(),
transformer_exog = None,
weight_func = None,
series_weights = None
)
# Grid search Multi Series
# ==============================================================================
lags_grid = [24, 48]
param_grid = {'alpha': [0.01, 0.1, 1]}
levels = ['item_1', 'item_2', 'item_3']
results = grid_search_forecaster_multiseries(
forecaster = forecaster,
series = data,
exog = None,
levels = levels,
lags_grid = lags_grid,
param_grid = param_grid,
steps = 24,
metric = 'mean_absolute_error',
initial_train_size = len(data_train),
refit = True,
fixed_train_size = True,
return_best = False,
verbose = False
)
results
6 models compared for 3 level(s). Number of iterations: 6.
lags grid: 0%| | 0/2 [00:00<?, ?it/s]
params grid: 0%| | 0/3 [00:00<?, ?it/s]
params grid: 0%| | 0/3 [00:00<?, ?it/s]
levels | lags | params | mean_absolute_error | alpha | |
---|---|---|---|---|---|
5 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 1} | 2.207648 | 1.00 |
4 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.1} | 2.207700 | 0.10 |
3 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.01} | 2.207706 | 0.01 |
2 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 1} | 2.335039 | 1.00 |
1 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.1} | 2.335149 | 0.10 |
0 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.01} | 2.335161 | 0.01 |
Weights in multi-series¶
The weights are used to control the influence that each observation has on the training of the model. ForecasterAutoregMultiseries
accepts two types of weights:
series_weights
controls the relative importance of each series. If a series has twice as much weight as the others, the observations of that series influence the training twice as much. The higher the weight of a series relative to the others, the more the model will focus on trying to learn that series.weight_func
controls the relative importance of each observation according to its index value. For example, a function that assigns a lower weight to certain dates.
If the two types of weights are indicated, they are multiplied to create the final weights. The resulting sample_weight
cannot have negative values.
series_weights
is a dict of the form{'series_column_name': float}
. If a series is used duringfit
and is not present inseries_weights
, it will have a weight of 1.weight_func
is a function that defines the individual weights of each sample based on the index.If it is a
callable
, the same function will apply to all series.If it is a
dict
of the form{'series_column_name': callable}
, a different function can be used for each series. A weight of 1 is given to all series not present inweight_func
.
# Weights in Multi-Series
# ==============================================================================
def custom_weights(index):
"""
Return 0 if index is between '2013-01-01' and '2013-01-31', 1 otherwise.
"""
weights = np.where(
(index >= '2013-01-01') & (index <= '2013-01-31'),
0,
1
)
return weights
forecaster = ForecasterAutoregMultiSeries(
regressor = Ridge(random_state=123),
lags = 24,
transformer_series = None,
transformer_exog = None,
weight_func = custom_weights,
series_weights = {'item_1': 1., 'item_2': 2., 'item_3': 1.} # Same as {'item_2': 2.}
)
forecaster.fit(series=data_train)
forecaster.predict(steps=24).head(3)
item_1 | item_2 | item_3 | |
---|---|---|---|
2014-07-16 | 25.547560 | 10.527454 | 11.195018 |
2014-07-17 | 24.779779 | 10.987891 | 11.424717 |
2014-07-18 | 24.182702 | 11.375158 | 13.090853 |
  Warning
The weight_func
and series_weights
arguments will be ignored if the regressor does not accept sample_weight
in its fit
method.
The source code of the weight_func
added to the forecaster is stored in the argument source_code_weight_func
. If weight_func
is a dict
, it will be a dict
of the form {'series_column_name': source_code_weight_func}
.
print(forecaster.source_code_weight_func)
def custom_weights(index): """ Return 0 if index is between '2013-01-01' and '2013-01-31', 1 otherwise. """ weights = np.where( (index >= '2013-01-01') & (index <= '2013-01-31'), 0, 1 ) return weights
Scikit-learn transformers in multi-series¶
Learn more about using scikit-learn transformers with skforecast.
- If
transformer_series
is atransformer
the same transformation will be applied to all series. - If
transformer_series
is adict
a different transformation can be set for each series. Series not present in the dict will not have any transformation applied to them.
forecaster = ForecasterAutoregMultiSeries(
regressor = Ridge(random_state=123),
lags = 24,
transformer_series = {'item_1': StandardScaler(), 'item_2': StandardScaler()},
transformer_exog = None,
weight_func = None,
series_weights = None
)
forecaster.fit(series=data_train)
forecaster
c:\Users\jaesc2\Miniconda3\envs\skforecast\lib\site-packages\skforecast\ForecasterAutoregMultiSeries\ForecasterAutoregMultiSeries.py:453: IgnoredArgumentWarning: {'item_3'} not present in `transformer_series`. No transformation is applied to these series. You can suppress this warning using: warnings.simplefilter('ignore', category=IgnoredArgumentWarning) warnings.warn(
============================ ForecasterAutoregMultiSeries ============================ Regressor: Ridge(random_state=123) Lags: [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24] Transformer for series: {'item_1': StandardScaler(), 'item_2': StandardScaler()} Transformer for exog: None Window size: 24 Series levels (names): ['item_1', 'item_2', 'item_3'] Series weights: None Weight function included: False Exogenous included: False Type of exogenous variable: None Exogenous variables names: None Training range: [Timestamp('2012-01-01 00:00:00'), Timestamp('2014-07-15 00:00:00')] Training index type: DatetimeIndex Training index frequency: D Regressor parameters: {'alpha': 1.0, 'copy_X': True, 'fit_intercept': True, 'max_iter': None, 'positive': False, 'random_state': 123, 'solver': 'auto', 'tol': 0.0001} fit_kwargs: {} Creation date: 2023-05-29 13:15:14 Last fit date: 2023-05-29 13:15:14 Skforecast version: 0.8.1 Python version: 3.10.11 Forecaster id: None
Compare multiple metrics¶
All three functions (backtesting_forecaster_multiseries
, grid_search_forecaster_multiseries
, and random_search_forecaster_multiseries
) allow the calculation of multiple metrics for each forecaster configuration if a list is provided. This list may include custom metrics and the best model selection is done based on the first metric of the list.
# Grid search Multi-Series with multiple metrics
# ==============================================================================
forecaster = ForecasterAutoregMultiSeries(
regressor = Ridge(random_state=123),
lags = 24
)
def custom_metric(y_true, y_pred):
"""
Calculate the mean absolute error using only the predicted values of the last
3 months of the year.
"""
mask = y_true.index.month.isin([10, 11, 12])
metric = mean_absolute_error(y_true[mask], y_pred[mask])
return metric
lags_grid = [24, 48]
param_grid = {'alpha': [0.01, 0.1, 1]}
results = grid_search_forecaster_multiseries(
forecaster = forecaster,
series = data,
lags_grid = lags_grid,
param_grid = param_grid,
steps = 24,
metric = [mean_absolute_error, custom_metric, 'mean_squared_error'],
initial_train_size = len(data_train),
fixed_train_size = True,
levels = None,
exog = None,
refit = True,
return_best = False,
verbose = False
)
results
6 models compared for 3 level(s). Number of iterations: 6.
lags grid: 0%| | 0/2 [00:00<?, ?it/s]
params grid: 0%| | 0/3 [00:00<?, ?it/s]
params grid: 0%| | 0/3 [00:00<?, ?it/s]
levels | lags | params | mean_absolute_error | custom_metric | mean_squared_error | alpha | |
---|---|---|---|---|---|---|---|
5 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 1} | 2.190420 | 2.290771 | 9.250861 | 1.00 |
4 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.1} | 2.190493 | 2.290853 | 9.251522 | 0.10 |
3 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.01} | 2.190500 | 2.290861 | 9.251589 | 0.01 |
2 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 1} | 2.282886 | 2.358415 | 9.770826 | 1.00 |
1 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.1} | 2.282948 | 2.358494 | 9.771567 | 0.10 |
0 | [item_1, item_2, item_3] | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14... | {'alpha': 0.01} | 2.282954 | 2.358502 | 9.771641 | 0.01 |
  Warning
bayesian_search_forecaster_multiseries
will be released in a future version of skforecast.
Stay tuned!
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