Python DatetimeIndex Error - TypeError: ("cannot do label indexing on <class 'pandas.tseries.index.DatetimeIndex'

Question

I have so far the following code provided by EdChum:

In [1]:
df = pd.DataFrame({'a': [None] * 6, 'b': [2, 3, 10, 3, 5, 8]})
df["c"] =np.NaN

df["c"][0] = 1
df["c"][2] = 3


def func(x):
    if pd.notnull(x['c']):
        return x['c']
    else:
        return df.iloc[x.name - 1]['c'] * x['b']
df['c'] = df.apply(func, axis =1)
df['c'] = df.apply(func, axis =1)
df['c'] = df.apply(func, axis =1)
df

Out[1]:
      a   b    c
0  None   2    1
1  None   3    3
2  None  10    3
3  None   3    9
4  None   5   45
5  None   8  360

That also works perfectly well, but as soon as I change the index of the dateframe = df as follows:

rng = pd.date_range('1/1/2011', periods=6, freq='D')

df = pd.DataFrame({'a': [None] * 6, 'b': [2, 3, 10, 3, 5, 8]},index=rng)

I get the following error: TypeError: ("cannot do label indexing on <class 'pandas.tseries.index.DatetimeIndex'> with these indexers [2011-01-01 00:00:00] of <class 'pandas.tslib.Timestamp'>", u'occurred at index 2011-01-02 00:00:00')

What is the problem here? How do I need to adjust the code in order to make it work with da DatetimeIndex?

Answer 1

The following works, the difference here is that I get the integer location of the datetime value in the index using get_loc:

In [48]:

rng = pd.date_range('1/1/2011', periods=6, freq='D')
df = pd.DataFrame({'a': [None] * 6, 'b': [2, 3, 10, 3, 5, 8]},index=rng)
df["c"] =np.NaN
​
df["c"][0] = 1
df["c"][2] = 3
​
​
def func(x):
    if pd.notnull(x['c']):
        return x['c']
    else:
        return df.iloc[df.index.get_loc(x.name) - 1]['c'] * x['b']
df['c'] = df.apply(func, axis =1)
df['c'] = df.apply(func, axis =1)
df['c'] = df.apply(func, axis =1)
df

Out[48]:
               a   b    c
2011-01-01  None   2    1
2011-01-02  None   3    3
2011-01-03  None  10    3
2011-01-04  None   3    9
2011-01-05  None   5   45
2011-01-06  None   8  360