Pandas: convert dtype 'object' to int

Question

I've read an SQL query into Pandas and the values are coming in as dtype 'object', although they are strings, dates and integers. I am able to convert the date 'object' to a Pandas datetime dtype, but I'm getting an error when trying to convert the string and integers.

Here is an example:

>>> import pandas as pd >>> df = pd.read_sql_query('select * from my_table', conn) >>> df     id    date          purchase  1  abc1  2016-05-22    1  2  abc2  2016-05-29    0  3  abc3  2016-05-22    2  4  abc4  2016-05-22    0  >>> df.dtypes  id          object  date        object  purchase    object  dtype: object 

Converting the df['date'] to a datetime works:

>>> pd.to_datetime(df['date'])  1  2016-05-22  2  2016-05-29  3  2016-05-22  4  2016-05-22  Name: date, dtype: datetime64[ns]  

But I get an error when trying to convert the df['purchase'] to an integer:

>>> df['purchase'].astype(int)  ....  pandas/lib.pyx in pandas.lib.astype_intsafe (pandas/lib.c:16667)()  pandas/src/util.pxd in util.set_value_at (pandas/lib.c:67540)()   TypeError: long() argument must be a string or a number, not 'java.lang.Long' 

NOTE: I get a similar error when I tried .astype('float')

And when trying to convert to a string, nothing seems to happen.

>>> df['id'].apply(str)  1 abc1  2 abc2  3 abc3  4 abc4  Name: id, dtype: object 

Answer 1

Documenting the answer that worked for me based on the comment by @piRSquared.

I needed to convert to a string first, then an integer.

>>> df['purchase'].astype(str).astype(int)