python - Comparing two pandas dataframes for differences

Question

I've got a script updating 5-10 columns worth of data , but sometimes the start csv will be identical to the end csv so instead of writing an identical csvfile I want it to do nothing...

How can I compare two dataframes to check if they're the same or not?

csvdata = pandas.read_csv('csvfile.csv')
csvdata_old = csvdata

# ... do stuff with csvdata dataframe

if csvdata_old != csvdata:
    csvdata.to_csv('csvfile.csv', index=False)

Any ideas?

Answer 1

You also need to be careful to create a copy of the DataFrame, otherwise the csvdata_old will be updated with csvdata (since it points to the same object):

csvdata_old = csvdata.copy()

To check whether they are equal, you can use assert_frame_equal as in this answer:

from pandas.util.testing import assert_frame_equal
assert_frame_equal(csvdata, csvdata_old)

You can wrap this in a function with something like:

try:
    assert_frame_equal(csvdata, csvdata_old)
    return True
except:  # appeantly AssertionError doesn't catch all
    return False

There was discussion of a better way...