'pandas how to swap or reorder columns

I know that there are ways to swap the column order in python pandas. Let say I have this example dataset:

import pandas as pd    
employee = {'EmployeeID' : [0,1,2],
     'FirstName' : ['a','b','c'],
     'LastName' : ['a','b','c'],
     'MiddleName' : ['a','b', None],
     'Contact' : ['(M) 133-245-3123', '(F)[email protected]', '(F)312-533-2442 [email protected]']}

df = pd.DataFrame(employee)

The one basic way to do would be:

neworder = ['EmployeeID','FirstName','MiddleName','LastName','Contact']
df=df.reindex(columns=neworder)

However, as you can see, I only want to swap two columns. It was doable just because there are only 4 column, but what if I have like 100 columns? what would be an effective way to swap or reorder columns?

There might be 2 cases:

when you just want 2 columns swapped.
when you want 3 columns reordered. (I am pretty sure that this case can be applied to more than 3 columns.)

Solution 1:^[1]

Say your current order of column is [b,c,d,a] and you want to order it into [a,b,c,d], you could do it this way:

new_df = old_df[['a', 'b', 'c', 'd']]

Solution 2:^[2]

When faced with same problem at larger scale, I came across a very elegant solution at this link: http://www.datasciencemadesimple.com/re-arrange-or-re-order-the-column-of-dataframe-in-pandas-python-2/ under the heading "Rearrange the column of dataframe by column position in pandas python".

Basically if you have the column order as a list, you can read that in as the new column order.

##### Rearrange the column of dataframe by column position in pandas python

df2=df1[df1.columns[[3,2,1,0]]]
print(df2)

In my case, I had a pre-calculated column linkage that determined the new order I wanted. If this order was defined as an array in L, then:

a_L_order = a[a.columns[L]]

Solution 3:^[3]

If you want to have a fixed list of columns at the beginning, you could do something like

cols = ['EmployeeID','FirstName','MiddleName','LastName']
df = df[cols + [c for c in df.columns if c not in cols]]

This will put these 4 columns first and leave the rest untouched (without any duplicate column).

Solution 4:^[4]

When writing to a file

Columns can also be reordered when the dataframe is written out to a file (e.g. CSV):

df.to_csv('employees.csv',
          columns=['EmployeeID','FirstName','MiddleName','LastName','Contact'])

Solution 5:^[5]

A concise way to reorder columns when you don't have too many columns and don't want to list the column names is with .iloc[].

df_reorderd = df.iloc[:, [0, 1, 3, 2, 4]]

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	sanster9292
Solution 2	rssmith01
Solution 3	Jean-Francois T.
Solution 4	Asclepius
Solution 5	jeffhale

'pandas how to swap or reorder columns

Solution 1:[1]

Solution 2:[2]

Solution 3:[3]

Solution 4:[4]