Conversion between columns and indexes of DataFrame objects of Pandas

Agreement:

import pandas as pd

Transformation between columns and indexes of DataFrame objects

Often we need to use a column or columns in an DataFrame object as an index, or convert the index into a column of the object. pandas provides set_index () /reset_index () for our use.

1. Convert columns to indexes

df1=pd.DataFrame({'X':range(5),'Y':range(5),'S':list("aaabb"),'Z':[1,1,2,2,2]})
df1

Code result:

	S	X	Y	Z
0	a	0	0	1
1	a	1	1	1
2	a	2	2	2
3	b	3	3	2
4	b	4	4	2

Specify Column Index

df1.set_index('S')

Code result:

	X	Y	Z
S
a	0	0	1
a	1	1	1
a	2	2	2
b	3	3	2
b	4	4	2

Specify multiple columns as multilevel indexes

df1.set_index(['S','Z'])

Code result:

		X	Y
S	Z
a	1	0	0
	1	1	1
	2	2	2
b	2	3	3
	2	4	4

While preserving columns as indexes

df1.set_index(['S','Z'],drop=False)

Code result:

		S	X	Y	Z
S	Z
a	1	a	0	0	1
	1	a	1	1	1
	2	a	2	2	2
b	2	b	3	3	2
	2	b	4	4	2

2. Convert indexes to columns

df2=df1.set_index(['S','Z'])
df2

Code result:

		X	Y
S	Z
a	1	0	0
	1	1	1
	2	2	2
b	2	3	3
	2	4	4

Use a single index as a column of an DataFrame object

df2.reset_index('Z')

Code result:

	Z	X	Y
S
a	1	0	0
a	1	1	1
a	2	2	2
b	2	3	3
b	2	4	4

Use multilevel indexes as columns

df2.reset_index()

Code result:

	S	Z	X	Y
0	a	1	0	0
1	a	1	1	1
2	a	2	2	2
3	b	2	3	3
4	b	2	4	4

Directly deletes the specified index

df2.reset_index('Z',drop=True)

Code result:

	X	Y
S
a	0	0
a	1	1
a	2	2
b	3	3
b	4	4

Modify the original DataFrame object directly

df2.reset_index(inplace=True)
df2

Code result:

	S	Z	X	Y
0	a	1	0	0
1	a	1	1	1
2	a	2	2	2
3	b	2	3	3
4	b	2	4	4