RPYS (Reference Publication Year Spectroscopy) Frame

>>> from techminer2.rpys import rpys_frame
>>> rpys_frame(
...     #
...     # DATABASE PARAMS:
...     root_dir="example/",
... ).head()
      Num References  Median
1957               1    -1.0
1958               0     0.0
1959               0     0.0
1960               0     0.0
1961               0     0.0