[ Python 常見問題 ] Pandas - How to find a minimum value in a pandas dataframe column ?

 Source From Here

Question
Examples of how to find a minimum value in a pandas dataframe column.

HowTo

Create a dataframe
Lets create for example a simple data frame:

view plaincopy to clipboardprint?

1. import pandas as pd  
2.   
3. data = {'Name':['Ben','Anna','Zoe','Tom','John','Steve','Becky','Bob'],   
4.         'Age':[36,27,20,12,30,20,22,21]}  
5.   
6. df = pd.DataFrame(data)  
7. df  

Output:

view plaincopy to clipboardprint?

1.     Name  Age  
2. 0    Ben   36  
3. 1   Anna   27  
4. 2    Zoe   20  
5. 3    Tom   12  
6. 4   John   30  
7. 5  Steve   20  
8. 6  Becky   22  
9. 7    Bob   21  

Find the min value in the column Age
To find the minimum value in the column Age, a solution is to use the pandas function min:

view plaincopy to clipboardprint?

1. df['Age'].min()  # Output: 12  

Find the index corresponding to the min value in the column Age
It is also possible to find the index corresponding to the min value in the column Age using the pandas function called idxmin:

view plaincopy to clipboardprint?

1. df['Age'].idxmin()  # Output: 3  

Then using the index above:

view plaincopy to clipboardprint?

1. df.iloc[3,:]  

Output:

view plaincopy to clipboardprint?

1. Name    Tom  
2. Age      12  
3. Name: 3, dtype: object  

An example with multiple rows with a min value in the same column
Lets create a dataframe with two min values in the column Age:

view plaincopy to clipboardprint?

1. import pandas as pd  
2.   
3. data = {'Name':['Ben','Anna','Zoe','Tom','John','Steve','Becky','Bob'],   
4.         'Age':[12,27,20,12,30,20,22,21]}  
5.   
6. df = pd.DataFrame(data)  
7.   
8. print(df)  

Output:

view plaincopy to clipboardprint?

1.     Name  Age  
2. 0    Ben   12  
3. 1   Anna   27  
4. 2    Zoe   20  
5. 3    Tom   12  
6. 4   John   30  
7. 5  Steve   20  
8. 6  Becky   22  
9. 7    Bob   21  

Then the function min:

view plaincopy to clipboardprint?

1. df['Age'].min()  # Output: 12  

however idxmin:

view plaincopy to clipboardprint?

1. df['Age'].idxmin()  # Output: 0  

To get rows with a min value in the column Age a solution is to do:

view plaincopy to clipboardprint?

1. df[ df['Age'] == df['Age'].min() ]  

Output:

view plaincopy to clipboardprint?

1.   Name  Age  
2. 0  Ben   12  
3. 3  Tom   12  

and to get the indexes:

view plaincopy to clipboardprint?

1. df[ df['Age'] == df['Age'].min() ].index  

which return:

view plaincopy to clipboardprint?

1. Int64Index([0, 3], dtype='int64')