[R] Unexpected behavior in par()

[Bill Dunlap]

par("mfrow") works by updating par("fig") before each plot.  I think that
when you reset all the par values after each plot you reset par("fig") to
the value it had before you made the last plot.

-Bill

On Sat, Apr 2, 2022 at 10:45 AM Rui Barradas <ruipbarradas using sapo.pt> wrote:

> Hello,
>
> I have a function using base graphics that changes some graphics
> parameters, then plots what it has to plot, then on exit puts the
> graphics parameters back as they were.
> The problem is that if outside the function the graphics parameters are
> also changed, for instance mfrow, those chages are not respected by the
> function. This seems to come from the way the graphics pars are saved.
>
> After par(mfrow = c(2, 1))
>
> - if I call par(no.readonly = TRUE) then the second call to the function
> plots in the 1st row, it overplots what was plotted before.
> - if I save the pars when they are changed, all is well.
>
> Here is a reproducible example.
>
>
> f <- function(x, ...) {
>    old_par <- par(no.readonly = TRUE)    # this is the problem
>    par(mar = c(4.1, 3.1, 3.1, 1.1))      # or maybe here
>    on.exit(par(old_par))
>    barplot(x, ...)
> }
>
> g <- function(x, ...) {
>    old_par <- par(mar = c(4.1, 3.1, 3.1, 1.1))   # this is the solution
>    on.exit(par(old_par))
>    barplot(x, ...)
> }
>
> set.seed(2022)
> b1 <- table(sample(4, 100, TRUE))
> b2 <- table(sample(10, 100, TRUE))
>
> # 1st function, unexpected behavior
> old_par <- par(mfrow = c(2, 1))
> f(b1, main = "1st plot")
> f(b2, main = "2nd plot")
> par(old_par)
>
> # 2nd function, all is well
> old_par <- par(mfrow = c(2, 1))
> g(b1, main = "1st plot")
> g(b2, main = "2nd plot")
> par(old_par)
>
>
> If I print(old_par) in any of the functions the result is the right
> mfrow setting, so I would expect the 2nd call to f() to plot in the 2nd
> row. But it doesn't.
> Function f() calls par() twice but it only changes a parameter unrelated
> to the parameter set outside the function.
>
> I'm obviously making a mistake but I don't know what. Is this expected
> (or a par() bug)?
>
>
> Thaks in advance,
>
> Rui Barradas
>
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