np.where has the semantics of a vectorized if/else (similar to Apache Spark's when/otherwise DataFrame method). I know that I can use np.where on pandas Series, but pandas often defines its own API to use instead of raw numpy functions, which is usually more convenient with pd.Series/pd.DataFrame.
Sure enough, I found pandas.DataFrame.where. However, at first glance, it has a completely different semantics. I could not find a way to rewrite the most basic example of np.where using pandas where:
# df is pd.DataFrame
# how to write this using df.where?
df['C'] = np.where((df['A'] < 0) | df['B'].isnull(), df['B'], df['A'])
Am I missing something obvious? Or is pandas where intended for a completely different use case, despite same name as np.where?