# [R] Mapping 2D to 3D

Jeff Newmiller jdnewm|| @end|ng |rom dcn@d@v|@@c@@u@
Sat Sep 19 06:42:46 CEST 2020

```When dealing with a 2-d density plot, the z variable is a predefined function of your x and y data, it is not something you can specify. If you want to specify z, then you need to use geom_contour. You appear to need to study the theory of kernel density estimates, which is off topic here. (Technically contributed packages like ggplot2 are off topic here also, though sometimes people will answer questions about them anyway.)

On September 18, 2020 6:34:43 PM PDT, H <agents using meddatainc.com> wrote:
>On 09/18/2020 02:26 AM, Jeff Newmiller wrote:
>> No, but fortunately you are off in the weeds. Density has an
>internally-computed "z" coordinate... you should be looking at
>?geom_contour.
>>
>> On September 17, 2020 7:17:33 PM PDT, H <agents using meddatainc.com>
>wrote:
>>> I am trying to understand how to map 2D to 3D using ggplot() and
>>> eventually plot_gg(). I am, however, stuck on understanding how to
>>> express the third variable to be mapped. This example:
>>>
>>> ggdiamonds = ggplot(diamonds, aes(x, depth)) +
>>> stat_density_2d(aes(fill = stat(nlevel)),
>>> geom = "polygon", n = 100, bins = 10,contour = TRUE) +
>>> facet_wrap(clarity~.) +
>>> scale_fill_viridis_c(option = "A")
>>>
>>> uses a variable nlevel that I now understand is calculated during
>the
>>> building of the ggplot but I have not figured out from where it is
>>> calculated or how to specify a variable of my choosing.
>>>
>>> Does anyone have a good reference for understanding how to specify
>this
>>> variable? Most examples on the 'net seem to use the same dataset but
>do
>>> not specify this particular aspect...
>>>
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>
>But looking at the code in my message above, how does one know what
>stat(nlevel) refers to? What if I wanted to map another variable in
>this particular dataset??
>
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