I have a datatable as -
DT = dt.Frame(
A=[1, 3, 2, 1, 4, 2, 1],
B=['A','B','C','A','D','B','A'],
C=['myamulla','skumar','cary','myamulla','api','skumar','myamulla'])
Out[14]:
| A B C
-- + -- -- --------
0 | 1 A myamulla
1 | 3 B skumar
2 | 2 C cary
3 | 1 A myamulla
4 | 4 D api
5 | 2 B skumar
6 | 1 A myamulla
[7 rows x 3 columns]
I'm now going to select an observation which has api in column C as -
DT[f.C=="api",:]
Out[12]:
| A B C
-- + -- -- ---
0 | 4 D api
OK,Now i would like to find an index related to this observation so that I can select the observation from this index onwards in datatable,
For example the above observation has got a row number 4 in DT, I can select the observations from 4th onwards as -
DT[4:,:]
Out[15]:
| A B C
-- + -- -- --------
0 | 4 D api
1 | 2 B skumar
2 | 1 A myamulla
But what if have millions of observations in DT, i can't figure out the required observation index.
One way around it is to create a temporary index column:
from datatable import dt, f, update
DT[:, update(index = range(DT.nrows))]
In [8]: DT
Out[8]:
| A B C index
| int32 str32 str32 int32
-- + ----- ----- -------- -----
0 | 1 A myamulla 0
1 | 3 B skumar 1
2 | 2 C cary 2
3 | 1 A myamulla 3
4 | 4 D api 4
5 | 2 B skumar 5
6 | 1 A myamulla 6
[7 rows x 4 columns]
Now create a filter in i to select the index downwards:
In [11]: DT[DT[f.C=='api', 'index'][0,0]:, :-1]
Out[11]:
| A B C
| int32 str32 str32
-- + ----- ----- --------
0 | 4 D api
1 | 2 B skumar
2 | 1 A myamulla
[3 rows x 3 columns]