ผู้ชมคนไหนมีภาษา troff (typesetter runoff) , groff (gnu runoff)?
Which viewers have the language of troff (typesetter runoff) , groff (gnu runoff)?
df = pd.DataFrame(columns=['viewer', 'language'])
df.loc[df['language'] == "troff (typesetter runoff) , groff (GNU runoff)", 'viewer']