Series astype() doesn't convert int64 to datetime64 using M8[D] anymore

[miketkelly]

add units='D' to Timestamp/to_datetime epoch support

I have an int64 series representing days since epoch which I'd like to convert to datetime64.
This works in 11.0 but raises an exception in 0.11.1.dev-964516a. The exception message is "TypeError: cannot convert datetimelike to dtype [datetime64[D]]".

import pandas as pd
s = pd.Series([0,1,2])
print s.astype('M8[D]')

My workaround is:

import pandas as pd
s = pd.Series([0,1,2])
print pd.Series(s.values.astype('M8[D]'))

[jreback]

this is on purpose, try this for converting from epoch (the docs for this are not fully merged yet):

I have never seen anyone specify epoch as you have an mean Days....what is the use case (most epcoh
is seconds, but usually ms)

In [6]: Series(pd.to_datetime([0,1,2],unit='s'))
Out[6]: 
0   1970-01-01 00:00:00
1   1970-01-01 00:00:01
2   1970-01-01 00:00:02
dtype: datetime64[ns]

I guess could add unit=D as well

In [25]: pd.to_datetime(pd.Series([0,1,2])*86400,unit='s')
Out[25]: 
0   1970-01-01 00:00:00
1   1970-01-02 00:00:00
2   1970-01-03 00:00:00
dtype: datetime64[ns]

[miketkelly]

In my use case I'm importing data from a SAS data set. SAS stores dates internally as the number of days since 1/1/1960. I could convert that into a string, and from a string into a datetime, but that's far slower than taking the value in as an int, adding a pre-computed number of days to adjust it to 1/1/1970, and then converting that int into a datetime with M8[D]. I can convert to seconds as you suggest, assuming leap seconds will always be ignored.

Thanks for your response. I'll close the case.

[jreback]

@mtkni ok to leave open....will leave this an open issue to add 'D' to units

though pandas/numpy will always be since 1/1/1970 (but that's a diff issue)

feel free to do a PR!

[jreback]

@mtkni we disabled the non-ns datetimetypes (and conversions from) because you can get really weird results ....hopefully units and friends will allow things like this

[jreback]

closed via #3973