Optimize adding of DataFrames

[oddaspa]

Is your feature request related to a problem? Please describe.
Adding (merging) of data frames is slow, making the data_frame endpoint appear slow.

Describe the solution you'd like
Optimize the merge function in data frames.

Describe alternatives you've considered
Use a cleaverer method and possibly introduce numpy.

Additional context
Add any other context or screenshots about the feature request here.