[R] Several quick questions

[deepayan.sarkar at gmail.com]

On 7/7/07, Sébastien <pomchip at free.fr> wrote:
> Dear R users,
>
> Here is a couple a quick questions, for which I was unable to not find
> any answer in the list archives and in the help:

[...]

> 2- When a log scale is called in a graph, the label takes a format like
> 10^n.

That's true for lattice, but not traditional graphics, as far as I know.

> Is there a way to come back to a regular number format like 1, 10,
> 100... without having to create a custom axis ?

Depends on what you mean by "custom axis". You don't need to manually
choose the tick positions etc, but you still need to define the rules
that determine how they are calculated. See example(axis.default) for
an example where the tick positions remain the same (as the defaults),
but the labels change.  The slightly different rule used in
traditional graphics is available through the axTicks() function,
which basically boils down to this:

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]]
}

where 'lim' is the limits in the original scale. So we have

> logTicks(c(1, 100))
[1]   1   5  10  50 100
> logTicks(c(1, 100), loc = c(2, 5, 10))
[1]   1   2   5  10  20  50 100

> 3- In lattice graphics, how does the default value of the "axs" argument
> influence the values of "limits" ?
> This question should be considered in the following context. The help
> states that a 4% extension is applied by default to the axis range in
> base graphics. So, I have tried to apply this 4 % extension to create
> some custom lattice graphics. I worked on a dataset in which the
> independent variable ranged from 0  to 120, so I basically customized my
> axis using limits=c(-4.8,124.8). The results of the graphics with and
> without the limits command were not identical...

The extension is user-settable in lattice, and defaults to 7% (I think
this value came from Trellis specs, but I don't remember the exact
details).

> lattice.getOption("axis.padding")
$numeric
[1] 0.07

$factor
[1] 0.6

-Deepayan