combine_predictions: Combining the predictions of several models
In vcerqueira/tsensembler: Dynamic Ensembles for Time Series Forecasting

This function simply applies a weighted average, where the predictions of the base models Y_hat are weighted according to their weights W. If a committee is specified, only models in the committee are weighted.

1	combine_predictions(Y_hat, W, committee = NULL)

`Y_hat`	a data.frame with the predictions of the base models;
`W`	a matrix or data.frame with the weights of the base models;
`committee`	A list containing the ids of the models in the committee.