can not convert column type from object to str in python dataframe

Question

i have downloaded a csv file, and then read it to python dataframe, now all 4 columns all have object type, i want to convert them to str type,

and now the result of dtypes is as follows:

Name                      object
Position Title            object
Department                object
Employee Annual Salary    object
dtype: object

i try to change the type using the following methods:

path['Employee Annual Salary'] = path['Employee Annual Salary'].astype(str)

but dtypes still return type object, and i also try to provide the column type when reading csv,

path = pd.read_csv("C:\\Users\\IBM_ADMIN\\Desktop\\ml-1m\\city-of-chicago-salaries.csv",dtype={'Employee Annual Salary':str})

or

path = pd.read_csv("C:\\Users\\IBM_ADMIN\\Desktop\\ml-1m\\city-of-chicago-salaries.csv",dtype=str)

but still do not work, want to know how to change column type from object to str,

Answer 1

Actually you can set the type of a column to string. Use .astype('string') rather than .astype(str).

Sample Data Set

df = pd.DataFrame(data={'name': ['Bla',None,'Peter']})

The column name is by default a object.

Single Column Solution

df.name = df.name.astype('string')

It's important to write .astype('string') rather than .astype(str) which didn't work for me. It will stay as object as you do so.

Multi-Column Solution

df = df.astype(dtype={'name': 'string'})

Allows to change multiple fields at once.

Answer 2

For strings, the column type will always be 'object.' There is no need for you convert anything; it is already doing what you require.

The types come from numpy, which has a set of numeric data types. Anything else is an object.

You might want to read http://nbviewer.jupyter.org/github/jakevdp/PythonDataScienceHandbook/blob/master/notebooks/02.01-Understanding-Data-Types.ipynb for a fuller explanation.