Use astype
You can use the astype
method to convert the dtype of a series to a NumPy dtype
df.time.astype('M8[us]')
There is probably a way to specify a Pandas style dtype as well (edits welcome)
Use map_partitions and meta
When using black-box methods like map_partitions
, dask.dataframe needs to know the type and names of the output. There are a few ways to do this listed in the docstring for map_partitions
.
You can supply an empty Pandas object with the right dtype and name
meta = pd.Series([], name="time", dtype=pd.Timestamp)
Or you can provide a tuple of (name, dtype)
for a Series or a dict for a DataFrame
meta = ('time', pd.Timestamp)
Then everything should be fine
df.time.map_partitions(pd.to_datetime, meta=meta)
If you were calling map_partitions
on df
instead then you would need to provide the dtypes for everything. That isn’t the case in your example though.