Trying to join 2 Dataframes, and store certain data as an array in one cell

Question

I have the following 3 data frames:

Frist dataframe:

DF1: 

iID data1 data2

10  blue  green

11  red   teal

Second dataframe:

Answer 1

IIUC

df1.merge(df2.groupby('iID').agg(lambda x : x.tolist()).reset_index())
Out[144]: 
   iID data1  data2        rH      repH
0   10  blue  green  [50, 60]  [60, 70]
1   11   red   teal      [70]      [50]

Answer 2

Worth to add below add ons..

join, which is left join by default:

df1.join(df2)

Or concat, which is outer join by default:

pd.concat([df1, df2], axis=1)

Just adding more narrative:

>>> df1 = pd.DataFrame({'a':range(6),
...                     'b':[5,3,6,9,2,4]}, index=list('abcdef'))
>>> df2 = pd.DataFrame({'c':range(4),
...                     'd':[10,20,30, 40]}, index=list('abhi'))
>>>
>>>
>>> df1
   a  b
a  0  5
b  1  3
c  2  6
d  3  9
e  4  2
f  5  4
>>> df2
   c   d
a  0  10
b  1  20
h  2  30
i  3  40
>>> df4 = df1.join(df2)
>>> df4
   a  b    c     d
a  0  5  0.0  10.0
b  1  3  1.0  20.0
c  2  6  NaN   NaN
d  3  9  NaN   NaN
e  4  2  NaN   NaN
f  5  4  NaN   NaN