Python pandas dict to csv with one header only-CodePudding

I have some data in a dict that I would like to save as an csv file with pandas:

data = {
        "a": 1,
        "c": 2,
        "d": 3,
       }

Which I am trying to save it in this format:

I am doing this with:

data = pd.DataFrame(data, index=[0])
data.to_csv(path, mode='a', columns=None, header=list(data.keys()))

After data is saved, I will have more entries (dict) that are in the same format as data that I need to append to the same csv file. Let's suppose I have:

data2 = {
        "a": 2,
        "c": 3,
        "d": 4,
       }

I need to append it as this:

But if I ran the same code with data2, the headers will be displayed again:

Is there a way to automatically add the header if it is the first entry, and for subsequent entries, no header will be added with the same code. I cannot detect in my code which data is the first entry.

CodePudding user response：

Only add the headers if the file does not exist:

import pandas
import os

data = pd.DataFrame({'a': [0], 'b': [1]})
data2 = pd.DataFrame({'a': [2], 'b': [3]})
path = './data.csv'

data.to_csv(path, mode='a', header=not os.path.exists(path))
data2.to_csv(path, mode='a', header=not os.path.exists(path))

CodePudding user response：

Use header=None after the first export:

data = pd.DataFrame(data, index=[0])
data.to_csv(path, mode='a')

data2 = pd.DataFrame(data2, index=[0])
data2.to_csv(path, mode='a', header=None)

Output:

,a,c,d
0,1,2,3
0,2,3,4

CodePudding user response：

To append new data without header just try to set header=False for next rows