def _febrl_links(df):
Get the links of a FEBRL dataset.
df_empty = df[[]].reset_index()
df_empty["key"] = df_empty["rec_id"].str. \
extract(r"rec-(\d+)", expand=True)[0]
// split the dataframe (org and dup)
org_bool = df_empty["rec_id"].str.endswith("org")
// merge the two frame and make MultiIndex.
pairs = df_empty[org_bool].merge(df_empty[~org_bool], on="key")
pairs_mi = pairs.set_index(["rec_id_x", "rec_id_y"]).index
pairs_mi.names = [None, None]
return pairs_mi