Multiple pandas.dataframe to one csv file

Question

I have multiple pandas dataframes, and hope to write them as one CSV file. What is the most straightforward way?

For example, from following four dataframes,

how can I create below CSV?

Note The dataframes all have the same dimensions.

Answer 1

A very straightforward way would be to concat pairs horizontally, concat the results vertically, and write it all out using to_csv:

 import pandas as pd

 pd.concat([
    pd.concat([df1, df2], axis=1),
    pd.concat([df3, df4], axis=1)]).to_csv('foo.csv')

---

A possibly more memory-conserving way would be to write it piecemeal:

with open('foo.csv', 'w') as f:
     pd.concat([df1, df2], axis=1).to_csv(f)
with open('foo.csv', 'a') as f:
     pd.concat([df3, df4], axis=1).to_csv(f, header=False)

Omitting headers=False would repeat the headers.

Answer 2

For anyone that needs to append multiple dataframes to same csv vertically, you can use this:

with open('all_dfs.csv','a') as f:
    for df in list_of_dfs:
        df.to_csv(f)
        f.write("\n")