First of all I am not sure if this is the correct title.
This is my DataFrame:

import pandas as pd
df = pd.DataFrame(
    {
        'a': [90, 102, 102, 150, 125, 115],
        'b': [98, 105, 90, 130, 102, 150],
        'label': list('abcdef')
    }
)

The expected output is creating column x:

     a    b    x
0   90   98   NaN
1  102  105   NaN
2  102   90   NaN
3  150  130   NaN
4  125  102     a
5  115  150     c

Basically I want to merge df with itself. I can get what I want with this code. I don’t know how to put words in order to convey what I want. I splitted df so that I have something to merge and then create x.

The splitted dataframes are df1 and df2.

df1 = df[['a', 'b']]
df2 = df[['a', 'label']].drop_duplicates(subset=['a'], keep='last')
df2['label'] = df2.label.shift(1)

df3 = df1.merge(df2, left_on='b', right_on='a', how='left', suffixes=['', '_y'])
df3 = df3.drop(columns=['a_y'])
df3 = df3.rename(columns={'label': 'x'})

Is there a more convenient way to get the same result?