pandas: merge/combine/update two dataframes

Question

I have 2 dataframes

   id  nr   lval
0   1  one     1
1   2  two     2
2   3  one     3

   id  nr  rval
4   1  one     4
5   2  one     5
6   3  one     6

I need merge or combine these two dataframes and use column 'id' as a key. By collision (column 'nr') take the column from first dataframe. Result should looks like this:

   id  nr   lval  rval
0   1  one     1     4
1   2  two     2     5
2   3  one     3     6

Answer 1

As the shapes of the dfs are the same you can call combine_first , the lhs df values supercede the rhs df hence you keep the nr column values:

In [3]:

df.combine_first(df1)
Out[3]:
   id  lval   nr  rval
0   1     1  one     4
1   2     2  two     5
2   3     3  one     6