[R] lattice logaritmic scale (basis "e" ), rewriting labels using xscale.component

[Deepayan Sarkar]

On 6/18/09, Katharina May <may.katharina at googlemail.com> wrote:
> Hi there,
>
>  sorry for troubling everybody once again, I've got a problem rewriting
>  Sarkar's function for
>  rewriting the tick locations in a logaritmic way (s.
>  http://lmdvr.r-forge.r-project.org/code/Chapter08.R):
>
>  His example works for log 2 but I need log e (natural logarithm). My
>  problem is that if I replace
>  2 with "e" (using paste()), I get the error message that the location
>  isn't a numeric value.

R doesn't have a constant that represents e, but

  tick.at <- logTicks(exp(lim), loc = c(1, 3))

instead of

  tick.at <- logTicks(paste("e^",lim,sep=""), loc = c(1, 3))

should give you e^lim. Or, if it makes it easier,

  e <- exp(1)
  tick.at <- logTicks(e^lim, loc = c(1, 3))

I don't think you need to change the logTicks function.

-Deepayan

>  Is there any way to get this working somehow or do I have to take a
>  different approach?
>
>  Thanks, Katharina
>
>  Here my failing approach:
>
>  require(lattice)
>  data(Earthquake, package = "MEMSS")
>
>  xscale.components.log <- function(lim, ...) {
>     ans <- xscale.components.default(lim = lim, ...)
>     tick.at <- logTicks(paste("e^",lim,sep=""), loc = c(1, 3))
>     ans$bottom$ticks$at <- log(tick.at, 2)
>     ans$bottom$labels$at <- log(tick.at, 2)
>     ans$bottom$labels$labels <- as.character(tick.at)
>     ans
>  }
>
>  logTicks <- function (lim, loc = c(1, 5)) {
>     ii <- floor(log(range(lim))) + c(-1, 2)
>     main <- paste("e^",(ii[1]:ii[2]),sep="")
>     r <- as.numeric(outer(loc, main, "*"))
>     r[lim[1] <= r & r <= lim[2]]
>  }
>  xyplot(accel ~ distance, data=Earthquake, scales = list(log = "e"),
>  xscale.components = xscale.components.log,
>
>
>
>
>  Here is the original  code of Sarkar:
>
>  logTicks <- function (lim, loc = c(1, 5)) {
>     ii <- floor(log10(range(lim))) + c(-1, 2)
>     main <- 10^(ii[1]:ii[2])
>     r <- as.numeric(outer(loc, main, "*"))
>     r[lim[1] <= r & r <= lim[2]]
>  }
>  xscale.components.log2 <- function(lim, ...) {
>     ans <- xscale.components.default(lim = lim, ...)
>     tick.at <- logTicks(2^lim, loc = c(1, 3))
>     ans$bottom$ticks$at <- log(tick.at, 2)
>     ans$bottom$labels$at <- log(tick.at, 2)
>     ans$bottom$labels$labels <- as.character(tick.at)
>     ans
>  }
>
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