You could try:

```
merge(d,m, by.x="v2", by.y="v3")
v2 v1 v4
1 A 1 a
2 A 7 a
3 B 4 b
4 B 5 b
5 C 3 c
6 C 6 c
7 E 2 e
8 E 8 e
```

## Edit

Here is another approach, to preserve the order:

```
data.frame(v1=d$v1, v4=m[match(d$v2, m$v3), 2])
v1 v4
1 1 a
2 2 e
3 3 c
4 4 b
5 5 b
6 6 c
7 7 a
8 8 e
```