r - Dynamic height and width for knitr plots

Question

In knitr, one can specify the size of plot by simply specifying it in the chunk options.

For example:

```{r, fig.width=9,fig.height=3}
plot(x)
```

I would like to be able to dynamically adjust the figure height and width on the basis of variables in x. Let's say that x is a data.frame:

x <- data.frame(x=factor(letters[1:3]),y=rnorm(3))

For example's sake lets say I would like to adjust fig.height to be equal to length(unique(x$x))

Answer 1

You can for example define the width in another chunk, then use it

```{r,echo=FALSE}
x <- data.frame(x=factor(letters[1:3]),y=rnorm(3))
len = length(unique(x$x))
```


```{r fig.width=len, fig.height=6}

plot(cars)
```