apply_levels: Converts the column factor levels in df to those in df_reference
Description
Each column in the result is a factor with the values of df and the levels of df_reference.
This means that if there are levels in df_to_change that are not in df_reference, NAs will be introduced.
The main use of this function is in classifier problems, where the training and the test set need to have equal factors.
To work, all names(df_reference) need to be
Usage
apply_levels(df, df_reference)
Arguments
df
The df that is to be releveled
df_reference
A reference df, which column levels will be applied to df if that column is a factor
Value
A data.frame where all factor's levels where changed. Through applying new levels, NAs could have been introduced