Mastering pandas - Second Edition

Implementation in pandas

In order to do the same thing in pandas, we read the CSV file saved in the preceding section:

    In [40]: flights_sample=pd.read_csv('nycflights13_sample.csv')
    
    In [41]: flights_sample.head()
    Out[41]: year   month   dep_delayarr_delay       distance
    0        2013   3       2       5       184
    1        2013   1       0       4       762
    2        2013   11      -7      -27     509
    3        2013   5       -5      -12     184
    4        2013   8       -1      -10     937
  

We achieve the same effect as ddply by making use of the GroupBy() operator, as shown in the following code and output:

    In [44]: pd.set_option('precision',3)
    In [45]: grouped = flights_sample_df.groupby(['year','month'])
    
    In [48]: grouped['dep_delay'].agg([np.mean, np.std])
    
    Out[48]:        mean    std
    year    month           
    2013    1       -0.20   2.28
            2       23.85   61.63
            3       10.00   34.72
            4       0.88    12.56
            5       8.56    32.42
     6 58.14 ...