How to save changes of Pandas data frame into a new file using pd.to_csv?

Asked Jan 30 '18 at 16:21

Active Nov 25 '19 at 14:48

Viewed 1,922 times

Trying to use a small example to explain my case:

df = pd.DataFrame([[1,1],[1,2],[1,3],[1,4]],columns=['A', 'B'])
d1 = df['B'].apply(lambda x: '{0:0>3}'.format(x))
df['B'] = d1
df.head()
df.to_csv()

I want to save changed df into a new csv file, which should be like:

Out[28]: A    B
      0  1  001
      1  1  002
      2  1  003
      3  1  004

But after saved it used df.to_csv(), the new data file has no changes:

Anyone could happy to tell how to fix it? many thanks!

edited Nov 25 '19 at 14:48

lczapski

asked Jan 30 '18 at 16:21

G.mc

how are you viewing the file? – Paul H Jan 30 '18 at 16:24
yes, I can viewed the new file which is same as the original one... – G.mc Jan 30 '18 at 17:16
I didn't ask if you could view the file. I asked how you were viewing the file. – Paul H Jan 30 '18 at 17:21
read this while you're at it: https://stackoverflow.com/questions/20109391/how-to-make-good-reproducible-pandas-examples – Paul H Jan 30 '18 at 17:22
Updated the question, thanks. – G.mc Jan 30 '18 at 20:17
Your code works fine for me. So again, I'll ask: *how* are you viewing the CSV after you've saved it? In a text editor? In Excel? – Paul H Jan 30 '18 at 22:43
I viewed it in Python, use of.read_csv. my actual file contains 2 more million rows... – G.mc Jan 31 '18 at 07:54
Using text editor viewed the saved file, it works. Why use python to view it does not work?? – G.mc Jan 31 '18 at 11:11
so your question is actually: "how to do I preserve leading zeros when I read in a CSV file with pandas?" – Paul H Jan 31 '18 at 16:33
looks like searching "pandas leading zeros" on this site turns up a lot of useful answers. – Paul H Jan 31 '18 at 16:37

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