official account ： Youer cottage
author ：Peter
edit ：Peter
Today, I would like to share a question about Pandas topic , Provide a variety of solutions ！
There is such a DataFrame（ The simulated data is ）, Find the index number of the first occurrence of each value ：
2 The first occurrence of index is 0
3 The first occurrence of index is 4
7 The first occurrence of index is 6
This is the final result to show , How to solve ？ Here are different solutions
shift The function moves the specified length in the specified axis direction ：
1、 First move down one unit , obtain df2
2、 For later processing ,df2 Rename the attribute field ：
df2.rename(columns={"col1":"col2"},inplace=True)3、 take df1 and df2 A merger
4、 Screening col1 and col2 Different situations can be
The complete line of code is as follows ：
Let's disassemble this line of code ：
1、 The difference function diff
Each data is subtracted from the previous value ; If two values are equal , The difference is 0
2、 Judgement and 0 The relationship between
3、 Lock to True The value of the can
A very clever way ： Direct weight removal , Keep the first piece of data ; But this is only a special case
The requirements are similar , Find the index of the first occurrence of each value ; But the data will appear repeatedly .
The correct results have been marked below ：
It can still be solved
result ：
It can also solve ：
But the de duplication function doesn't work in this case ：drop_duplicates A function is a de duplication of the overall data , Keep only one piece of data
Here we will focus on understanding the shift function shift Sum difference function diff The relationship between , Simulate a piece of data ：
Take the example of moving one unit by default
Conclusion ： Under the same conditions , Original data frame Subtract shift The data generated by the function is diff The result of the function
Under what circumstances will the shift or difference function be used ？
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