Comparing value with previous row in Pandas DataFrame

Issue

import pandas as pd
data={'col1':[1,3,3,1,2,3,2,2]}
df=pd.DataFrame(data,columns=['col1'])
print df


     col1  
0     1          
1     3          
2     3          
3     1          
4     2          
5     3          
6     2          
7     2      

I have the following Pandas DataFrame and I want to create another column that compares the previous row of col1 to see if the value of the row is greater than that of the previous row. It should come out like the following:

    col1  match  
0     1   False     
1     3   False     
2     3   True     
3     1   False     
4     2   False     
5     3   True     
6     2   False     
7     2   True 

Thank you.

Solution

Compare shifted values by Series.gt and Series.shift,last missing value is replaced to -1 for True, working, if all values are positive:

df['match'] = df['col1'].gt(df['col1'].shift(-1, fill_value=-1))
print (df)

   col1  match
0     1  False
1     3  False
2     3   True
3     1  False
4     2  False
5     3   True
6     2  False
7     2   True

If need last value set to True for any Dataframe:

df['match'] = df['col1'].gt(df['col1'].shift(-1))
df.loc[df.index[-1], 'match'] = True
    

Answered By – jezrael

This Answer collected from stackoverflow, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0