np.argwhere bug when applied to Pandas dataframes

Created by: igabriel85

Initially np.argwhere is applied on Pandas dataframes for prediction, this is no longer supported. Current workaround is to convert from Pandas to Numpy and then back again. More elegant solution is required.

Note: Other Numpy and Pandas methods such as np.where and df.where don't have the same outcome or are much slower than current solution.