How to add pandas data to an existing csv file?

I want to know if it is possible to use the pandas to_csv() function to add a dataframe to an existing csv file. The csv file has the same structure as the loaded data.

You can append to a csv by opening the file in append mode:

    with open('my_csv.csv', 'a') as f:
        df.to_csv(f, header=False)

If this was your csv, foo.csv:

    ,A,B,C
    0,1,2,3
    1,4,5,6

If you read that and then append, for example, df + 6:

    In [1]: df = pd.read_csv('foo.csv', index_col=0)

    In [2]: df
    Out[2]:
       A  B  C
    0  1  2  3
    1  4  5  6

    In [3]: df + 6
    Out[3]:
        A   B   C
    0   7   8   9
    1  10  11  12

    In [4]: with open('foo.csv', 'a') as f:
                 (df + 6).to_csv(f, header=False)

foo.csv becomes:

    ,A,B,C
    0,1,2,3
    1,4,5,6
    0,7,8,9
    1,10,11,12

From: stackoverflow.com/q/17530542

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