df['ciinstall'] = pd.to_datetime(df['ciinstall'])
df['cainstdate'] = pd.to_datetime(df['cainstdate'])
df = df.loc[(df['cainstdate']>= '2021-01-01') & (df['cainstdate']< '2022-01-01')]
df['gap'] = df['ciinstall'] - df['cainstdate']
df['gap'] = pd.to_numeric(df['gap'].dt.days, downcast='integer')
df = df.loc[df['gap'] < -365]