[R] Why does plot() ignore the data type for axis labels?

[Gavin Simpson]

On Tue, 2008-02-19 at 09:17 -0800, Stiffler wrote:
> Hello,
> 
> I was wondering why the plot() command ignores the datatype when displaying
> axis labels.  More specifically, if the data points are integers then the
> axis labels should intuitively also be integers, right?
> 
> > x <- as.integer(c(1,2,3))
> > y <-x
> > typeof(x)
> [1] "integer"
> > plot(x,y)
> >
> 
> The axis labels are 1.0, 1.5, 2.0, 2.5, 3.0  but if the integer type were
> taken into account they would be 1, 2, 3.

It is due to pretty() finding nice numbers for the axis

> pretty(x)
[1] 1.0 1.5 2.0 2.5 3.0

> 
> PS what's the right way to get integer labels?

Do them by hand, if they are (numeric) integers

> plot(x,y, axes = FALSE)
> axis(2)
> axis(1, at = x)
> box()

You could try writing your own Axis.integer function if doing the extra
steps is a pain - something like:

Axis.integer <- function(x = NULL, at = NULL, ..., side, labels = NULL) 
{
    at <- unique(x)
    labels <- as.character(at)
    axis(side = side, at = unique(x), labels = labels, ...)
}

which works in these case,

y2 <- runif(3)
plot(x, y)
plot(x, y2)

But is far from bullet proof and is not guaranteed to work in all
situations.

HTH

G

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