Select rows at specific multiindex level

Question

I have a dataframe with a multiindex, and i need to drop the first row from each piece of the first index.

                        cshoc   prccd       mkt_val    return
gvkey  datadate
001075 2019-01-29  112080000.0   87.36  9.791309e+09  0.006916
       2019-01-30  112080000.0   87.62  9.820450e+09  0.002976
       2019-01-31  112080000.0   88.12  9.876490e+09  0.005706
       2019-02-01  112080000.0   87.65  9.823812e+09 -0.005334
       2019-02-04  112080000.0   87.53  9.810362e+09 -0.001369
...                        ...     ...           ...       ...
316056 2020-01-21   92917000.0  127.14  1.181347e+10 -0.007107
       2020-01-22   92917000.0  129.45  1.202811e+10  0.018169
       2020-01-23   92917000.0  129.80  1.206063e+10  0.002704
       2020-01-24   92917000.0  128.00  1.189338e+10 -0.013867
       2020-01-27   92917000.0  127.67  1.186271e+10 -0.002578`

For example, the code would drop the rows at datadate = '2019-01-29' and '2020-01-21'. The first row will always have a different 'datadate' index value, so i can't choose specific values.

I have tried methods like .iloc[:,1:], .iloc[:,:,1:], and things with IndexSlice. So far, nothing has worked.

Any help would be appreciated!

Answer 1

tail

df.groupby(level=0).apply(lambda d: d.tail(-1))

Answer 2

You may also try this

df[df.index.get_level_values(0).duplicated()]

Out[262]:
                         cshoc   prccd       mkt_val      return
gvkey  datadate
1075   2019-01-30  112080000.0   87.62  9.820450e+09    0.002976
       2019-01-31  112080000.0   88.12  9.876490e+09    0.005706
       2019-02-01  112080000.0   87.65  9.823812e+09   -0.005334
       2019-02-04  112080000.0   87.53  9.810362e+09   -0.001369
316056 2020-01-22   92917000.0  129.45  1.202811e+10    0.018169
       2020-01-23   92917000.0  129.80  1.206063e+10    0.002704
       2020-01-24   92917000.0  128.00  1.189338e+10   -0.013867
       2020-01-27   92917000.0  127.67  1.186271e+10  -0.002578`

---

Note : as @piRSquared's comment, on one-row group of index level=0, this solution will not drop it. It still keeps that one row while @piRSquared's solution will drop that group completely.