Python Pandas Merge data from different Dataframes on specific index and create new one

Question

My code is given below: I have two data frames a,b. I want to create a new data frame c by merging a specific index data of a, b frames.

import pandas as pd
a = [10,20,30,40,50,60]
b = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6]
a = pd.DataFrame(a,columns=['Voltage'])
b = pd.DataFrame(b,columns=['Current'])
c = pd.merge(a,b,left_index=True, right_index=True)
print(c)

The actual output is:

     Voltage  Current
0       10      0.1
1       20      0.2
2       30      0.3
3       40      0.4
4       50      0.5
5       60      0.6

I don't want all the rows. But, specific index rows something like:

c =      Voltage Current
     0     30      0.3
     1     40      0.4

How to modify c = pd.merge(a,b,left_index=True, right_index=True) code so that, I only want those specific third and fourth rows in c with new index order as given above?

jezrael · Accepted Answer · 2018-08-14 09:03:16Z

2

Use iloc for select rows by positions and add reset_index with drop=True for default index in both DataFrames:

Solution1 with concat:

c = pd.concat([a.iloc[2:4].reset_index(drop=True),
               b.iloc[2:4].reset_index(drop=True)], axis=1)

Or use merge:

c = pd.merge(a.iloc[2:4].reset_index(drop=True),
             b.iloc[2:4].reset_index(drop=True), 
             left_index=True, 
             right_index=True)

print(c)
   Voltage  Current
0       30      0.3
1       40      0.4

edited Aug 14, 2018 at 9:03

answered Aug 14, 2018 at 8:54

jezrael

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13 Comments

Msquare Over a year ago

Excellent. It worked. Could you please, explain the significance or meaning of drop=True, axis=1 in concat code? Also, could you explain the significance or meaning of left-Index=True,right_index=True in Merge code?

jezrael Over a year ago

OK, the best for drop=True is try remove it like c = pd.concat([a.iloc[2:4], b.iloc[2:4]], axis=1), then get not 0,1 index but 2,3

Msquare Over a year ago

Ok. What about a.iloc'? I heard about a.loc? I mean, loc` and iloc are different?

jezrael Over a year ago

axis=1 in concat mean you want join by columns, check docs The axis to concatenate along and similar for merge it join by both indexes.

jezrael Over a year ago

@Msquare - I think better is is explained here

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