I am working with the R programming language. I am trying to follow the tutorial on "contour maps" posted over here: 2D contours of a 3D surface — geom_contour • ggplot2

I generated some data for this example:

```
#generate data
a <- rnorm(100,10,10)
b <- rnorm(100,5,5)
c <- rnorm(100,1,1)
d - data.frame(a,b,c)
```

Then, I tried to make these plots:

```
library(ggplot2)
v <- ggplot(d, aes(a, b, z = density))
v + geom_contour_filled()
```

But this produces the following warning messages:

```
Warning messages:
1: stat_contour(): Zero contours were generated
2: In min(x) : no non-missing arguments to min; returning Inf
3: In max(x) : no non-missing arguments to max; returning -Inf
```

And produces an empty plot instead of the desired plot:

Can someone please show me what I am doing wrong?

Thanks