
        
        
            
                
                
                    s = pd.Series([7,4,5,6], index=["a","b","c","d"])
s[s == 5]   # returns a Series
                
            
            c    5
dtype: int64

Duplicate case

For the duplicate case:


        
        
            
                
                
                    s = pd.Series([7,4,5,5], index=["a","b","c","d"])
s[s == 5]
                
            
            c    5
d    5
dtype: int64

Non-existent case

When the value you are finding does not exist, you get an empty Series:


        
        
            
                
                
                    s = pd.Series([7,4,5,6], index=["a","b","c","d"])
s[s == 8]
                
            
            Series([], dtype: int64)

Integer Index

Unique case

To get the integer index of a value in a Series, first convert the Series into an Index, and then use the get_loc(~) method:


        
        
            
                
                
                    s = pd.Series([7,4,5,6], index=["a","b","c","d"])
pd.Index(s).get_loc(5)
                
            
            2

Duplicate case

When there are duplicates, we get a NumPy array of booleans where True indicates the location of the value:


        
        
            
                
                
                    s = pd.Series([7,4,5,5], index=["a","b","c","d"])
pd.Index(s).get_loc(5)
                
            
            array([False, False,  True,  True])

If you want a list of integer indices instead of this boolean mask, use NumPy's where(~) method instead:


        
        
            
                
                
                    s = pd.Series([7,4,5,5], index=["a","b","c","d"])
np.where(s==5)
                
            
            (array([2, 3]),)

Non-existent case

If the value does not exist, we get a KeyError:


        
        
            
                
                
                    s = pd.Series([7,4,5,6], index=["a","b","c","d"])
pd.Index(s).get_loc(9)
                
            
            KeyError: 9

Published by Isshin Inada

Edited by 0 others

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