JP. JP. - 4 months ago 11
Python Question

Pandas Dataframe - Lookup Error

I am attempting to lookup a row in a pandas (version 0.14.1) dataframe using a date and stock ticker combination and am receiving a strange error.

My pandas dataframe that looks like this:

AAPL IBM GOOG XOM Date
2011-01-10 16:00:00 340.99 143.41 614.21 72.02 2011-01-10
2011-01-11 16:00:00 340.18 143.06 616.01 72.56 2011-01-11
2011-01-12 16:00:00 342.95 144.82 616.87 73.41 2011-01-12
2011-01-13 16:00:00 344.20 144.55 616.69 73.54 2011-01-13
2011-01-14 16:00:00 346.99 145.70 624.18 74.62 2011-01-14
2011-01-18 16:00:00 339.19 146.33 639.63 75.45 2011-01-18
2011-01-19 16:00:00 337.39 151.22 631.75 75.00 2011-01-19


When I attempt to do a lookup using a date/string combination I receive the following error:

>>> df_data.lookup(date,ticker)
Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/IPython/core/interactiveshell.py", line 2820, in run_code
exec code_obj in self.user_global_ns, self.user_ns
File "<ipython-input-2-31ab981e2184>", line 1, in <module>
df_data.lookup(date,ticker)
File "/usr/local/lib/python2.7/dist-packages/pandas/core/frame.py", line 2207, in lookup
n = len(row_labels)
TypeError: object of type 'datetime.datetime' has no len()


From what I can see in the pandas documentation, this should work and my date variable is a regular date time

>>> date
Out[5]: datetime.datetime(2011, 1, 10, 16, 0)


Am I doing something obviously incorrect?

Answer

df.lookup expects 2 array-likes (instead of scalars) as arguments:

In [25]: df.lookup(row_labels=[DT.datetime(2011,1,10,16,0)], col_labels=['AAPL'])
Out[25]: array([ 340.99])

If you only want to look up one value, use df.get_value instead:

In [30]: df.get_value(DT.datetime(2011,1,10,16,0), 'AAPL')
Out[30]: 340.99000000000001