[R] help--kernel distribution dynamics

Deepayan Sarkar deepayan at stat.wisc.edu
Sat Aug 23 18:39:22 CEST 2003

On Saturday 23 August 2003 10:36, Eugene Salinas wrote:
> Deall all,
> I'm just learning R, but unfortunately I need to
> urgently do a rather more complex task so I need some
> help. I have just learnt the very basics a few days
> ago and am not ready yet to deal with panels and
> kernel densities, so a soft guidance would be most
> appreciated.
> I have a (very) large panel data set (400,000
> individuals x50 time periods) and need to display the
> evolution of the kernel density of some of the
> variables over time. I can do slices in STATA - eg the
> distribution in 1950 and 1990 but they are difficult
> to compare due to different scales used. So I need to
> have a nice 3D graph that shows how the distribution
> evolved over time and am hoping that R can do it.
> I'm very grateful for any suggestions, eugene.

As a first step, you could create a matrix (with 50 rows, one for each time 
point) where each row holds the kernel density estimate for that time point. 
e.g. (with a grid of size 100 for each estimated density),

foo <- matrix(0, 50, 100)
for (i in 1:50) 
    foo[i, ] <- density(rnorm(5000), from = -4, to = 4, n = 100)$y
                        ^^^^^^^^^^^        ^^^^^^^^^^^
                         put your        put appropriate 
                       variable here          ranges

Whether a 3D view of this will be very informative will depend on your data 
(maybe you could play with the density() parameters), but persp() should give 
you something:

persp(foo, theta = 135, phi = 30, scale = FALSE,
      ltheta = -120, shade = 0.75, border = NA)



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