infer_freq on a series

[jseabold]

Somewhat related to #6273 . I'm fairly certain though not positive that this also used to work on 0.12.x.

df = pd.DataFrame(np.random.rand(5,3))
df['date'] = ['1-1-1990', '2-1-1990', '3-1-1990', '4-1-1990', '5-1-1990']
pd.infer_freq(df['date'])

Raises Series has no attribute is_monotonic. I guess infer_freq now expects either an Index or ....?

[22]: pd.version.version
[22]: '0.13.0-472-g9109812'

[jreback]

#6275 will close this as well (its the same issue)