In R: How can I insert a small data frame into a bigger one and simultaneously add new rows if necessary? The data frames should normally be merged by ID1, ID2 and ID3. But the bigger data frame got all row names of the smaller one.

Main data frame to be inserted in (NAs are left blank):

```
ID1  ID2  ID3  r1  r2  r3  r4  r5  r6
 A    1    a       d1
 A    1    b       d2
 A    2    a       d3

```

Small data frame:

```
ID1  ID2  ID3  r5
 A    1    a   d4
 A    1    b   d5
 A    2    a   d6
 A    2    b   d7

```

Desired output:

```
ID1  ID2  ID3  r1  r2  r3  r4  r5  r6
 A    1    a       d1          d4
 A    1    b       d2          d5
 A    2    a       d3          d6
 A    2    b                   d7

```