Slice Pandas DataFrame by Row

Question

I am working with survey data loaded from an h5-file as hdf = pandas.HDFStore('Survey.h5') through the pandas package. Within this DataFrame, all rows are the results of a single survey, whereas the columns are the answers for all questions within a single survey.

I am aiming to reduce this dataset to a smaller DataFrame including only the rows with a certain depicted answer on a certain question, i.e. with all the same value in this column. I am able to determine the index values of all rows with this condition, but I can't find how to delete this rows or make a new df with these rows only.

Solution 1

In [36]: df
Out[36]:
   A  B  C  D
a  0  2  6  0
b  6  1  5  2
c  0  2  6  0
d  9  3  2  2

In [37]: rows
Out[37]: ['a', 'c']

In [38]: df.drop(rows)
Out[38]:
   A  B  C  D
b  6  1  5  2
d  9  3  2  2

In [39]: df[~((df.A == 0) & (df.B == 2) & (df.C == 6) & (df.D == 0))]
Out[39]:
   A  B  C  D
b  6  1  5  2
d  9  3  2  2

In [40]: df.ix[rows]
Out[40]:
   A  B  C  D
a  0  2  6  0
c  0  2  6  0

In [41]: df[((df.A == 0) & (df.B == 2) & (df.C == 6) & (df.D == 0))]
Out[41]:
   A  B  C  D
a  0  2  6  0
c  0  2  6  0

Solution 2

If you already know the index you can use .loc:

In [12]: df = pd.DataFrame({"a": [1,2,3,4,5], "b": [4,5,6,7,8]})

In [13]: df
Out[13]:
   a  b
0  1  4
1  2  5
2  3  6
3  4  7
4  5  8

In [14]: df.loc[[0,2,4]]
Out[14]:
   a  b
0  1  4
2  3  6
4  5  8

In [15]: df.loc[1:3]
Out[15]:
   a  b
1  2  5
2  3  6
3  4  7

Comments

[yoshiserry]

is it possible to slice the dataframe and say (c = 5 or c =6) like THIS: ---> df[((df.A == 0) & (df.B == 2) & (df.C == 5 or 6) & (df.D == 0))]

[Wouter Overmeire]

df[((df.A == 0) & (df.B == 2) & df.C.isin([5, 6]) & (df.D == 0))] or df[((df.A == 0) & (df.B == 2) & ((df.C == 5) | (df.C == 6)) & (df.D == 0))]

[Phoenix Meadowlark]

It's worth a quick note that despite the notational similarity between df.loc[1:3] and some_list[1:3], the first uses an inclusive upper index while the second (and most of python) uses an exclusive upper index.