Converting Dataset from string to float error

Question

I have a dataset with 3 columns. In line1 of code, I replace the '%' with an empty value. In line2, I turn the international_students column string values into a float.

All good if I run the code once. However, if I run the code twice, I get an error: "Can only use .str accessor with string values, which use np.object_ dtype in pandas". I think it's because the column has turned into a float already.

How can I write the code so I can run it multiple times without the error?

df = pd.DataFrame({'university': ['harvard', 'cambridge', 'GT'],
                 'international_students': ['28%', '33%', '55%'],
                 index=['0', '1', '2']})

[line1]: df['international_students'] = df['international_students'].str.replace('%', '')
[line2]: df['international_students'] = df['international_students'].astype(np.float)

Onel Harrison · Accepted Answer · 2017-06-10 22:04:59Z

1

After running your code once, you've already converted the values to np.floats so running a str.replace again will definitely as fail, as expected.

If you want to do these operations multiple times, I would recommend that you create copies of your data using df.copy().

Example

original_df = pd.DataFrame({'university': ['harvard', 'cambridge', 'GT'],
                 'international_students': ['28%', '33%', '55%']},
                 index=['0', '1', '2'])

# use this copy for your operations involving using the international_student field
# as floats
odf_cp1 = original_df.copy()
odf_cp1['international_students'] = odf_cp1['international_students'].str.replace('%', '')
odf_cp1['international_students'] = odf_cp1['international_students'].astype(np.float)

edited Jun 10, 2017 at 22:04

answered Jun 10, 2017 at 21:58

Onel Harrison

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2 Comments

Adam Schroeder Over a year ago

Thank you Onel. Now I understand. Thank you for your help.

Onel Harrison Over a year ago

You're welcome. Since this solved your problem, go ahead and mark this as the answer.

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