[R] What's box() (exactly) doing?

[Jim Lemon]

Hi Marius,
There are a few things that are happening here. First, the plot area
is not going to be the same as your x and y limits unless you say so:

# run your first example
par("usr")
[1] -0.04  1.04 -0.04  1.04

# but
plot(NA, type = "n", ann = FALSE, axes = FALSE,
 xlim = 0:1, ylim = 0:1,xaxs="i",yaxs="i")
box()
rect(xleft = 0, ybottom = 0, xright = 1, ytop = 1, col = "grey80")
par("usr")
[1] 0 1 0 1

Second, the "rect" function is automatically clipped to the plot area,
so you may lose a bit at the edges if you don't override this:

par(xpd=TRUE)
rect(...)
par(xpd=FALSE)

Finally your second example simply multiplies the first problem by
specifying a layout of more than one plot. Applying the "xaxs" and
"yaxs" parameters before you start plotting will fix this:

par(xaxs="i",yaxs="i")

Jim

On Fri, Jun 24, 2016 at 12:29 PM, Marius Hofert
<marius.hofert at uwaterloo.ca> wrote:
> Hi,
>
> I would like to replicate the behavior of box() with rect() (don't ask why).
> However, my rect()angles are always too small. I looked a bit into the
> internal C_box but
> couldn't figure out how to solve the problem. Below is a minimal
> working (and a slightly bigger) example.
>
> Cheers,
> Marius
>
> ## MWE
> plot(NA, type = "n", ann = FALSE, axes = FALSE, xlim = 0:1, ylim = 0:1)
> rect(xleft = 0, ybottom = 0, xright = 1, ytop = 1, col = "grey80") #
> should match box()
> box()
>
> ## Extended example
>
> ## Basic plot
> my_rect <- function()
> {
>     plot(NA, type = "n", ann = FALSE, axes = FALSE, xlim = 0:1, ylim = 0:1)
>     rect(xleft = 0, ybottom = 0, xright = 1, ytop = 1, col = "grey80")
> # should match box()
>     box()
> }
>
> ## Layout
> lay <- matrix(0, nrow = 3, ncol = 3, byrow = TRUE)
> lay[1,1] <- 1
> lay[2,1] <- 2
> lay[2,2] <- 3
> lay[2,3] <- 4
> lay[3,3] <- 5
> layout(lay, heights = c(1, 10, 1), widths = c(10, 1, 10))
> layout.show(5) # => no space between rectangles; calls box() to draw the boxes
>
> ## Fill layout
> par(oma = rep(0, 4), mar = rep(0, 4))
> my_rect()
> my_rect()
> my_rect()
> my_rect()
> my_rect()
> ## => spaces between rectangles => why?/how to avoid?
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.