I have 3 dataframes that I would like to bind together by row but also retain the columns that each one has such that columns not present in one dataframe are just initialized to NA and added to the resultant dataframe. Since I may have many more columns than the ones provided in the example below, I can't hardcode them as I have been doing so far.

```
a=data.frame(v1=rnorm(10),v2=rnorm(10),v3=rnorm(10))

b=data.frame(v1=rnorm(10),v3=rnorm(10),v4=rnorm(10))

c=data.frame(v2=rnorm(10),v5=rnorm(10),v6=rnorm(10))

```

**Desired output:**

Dimensions of 30 by 6 with an output header of

```
v1    v2    v3    v4    v5    v6
0.0.. 0.0.. 0.0.. NA    NA    NA
0.0.. NA    0.0.. 0.0.. NA    NA
NA    0.0.. NA    NA    0.0.. 0.0..
etc.

```

How do I achieve this in a scaleable and efficient way?