[R] Getting the values out of histogram (lattice)

[Rolf Turner]

On 05/09/11 21:26, Deepayan Sarkar wrote:


<SNIP>
> 1. The `official' way to get panel arguments is trellis.panelArgs(); e.g.,
>
>> p<- histogram(~rnorm(100) | gl(2, 50), type = "density")
>> str(trellis.panelArgs(p, 2))
> List of 5
>   $ x           : num [1:50] 0.277 1.144 1.13 -0.912 -0.892 ...
>   $ breaks      : num [1:9] -2.561 -1.979 -1.398 -0.816 -0.234 ...
>   $ type        : chr "density"
>   $ equal.widths: logi TRUE
>   $ nint        : num 8
>
> 2. hist.constructor() is needed for technical reasons, and can be
> considered to be the same as hist() for this purpose. So the
> computations performed by panel.histogram() can be reduced to
>
>
> histogram.computations<-
>      function(x, breaks, equal.widths = TRUE,
>               type = "density", nint, ...)
> {
>      if (is.null(breaks))
>      {
>          breaks<-
>              if (is.factor(x)) seq_len(1 + nlevels(x)) - 0.5
>              else if (equal.widths) do.breaks(range(x, finite = TRUE), nint)
>              else quantile(x, 0:nint/nint, na.rm = TRUE)
>      }
>      hist(x, breaks = breaks, plot = FALSE)
> }
>
> which may be used as follows to get the ``actual data defining the histogram'':
>
>> a<- trellis.panelArgs(p, 2)
>> h<- do.call(histogram.computations, a)
>> str(h)
> List of 7
>   $ breaks     : num [1:9] -2.561 -1.979 -1.398 -0.816 -0.234 ...
>   $ counts     : int [1:8] 1 4 6 14 7 8 6 4
>   $ intensities: num [1:8] 0.0344 0.1375 0.2062 0.4812 0.2406 ...
>   $ density    : num [1:8] 0.0344 0.1375 0.2062 0.4812 0.2406 ...
>   $ mids       : num [1:8] -2.2704 -1.6885 -1.1065 -0.5246 0.0573 ...
>   $ xname      : chr "x"
>   $ equidist   : logi TRUE
>   - attr(*, "class")= chr "histogram"

As usual:  Clear, concise, and useful!  Thanks!

     cheers,

         Rolf