ggplot stat smooth and poly

Dear all

I am not sure, but I believe that in past it was possible to add smoothing
lines in ggplot even if some group did not have enough points to perform
calculation (although I did not find any version which could deliver it).

Here is the code and data

library(ggplot2)
p <- ggplot(test, aes(x=one, y=two, colour=three))
p+geom_point(size=5)+stat_smooth(method="lm")
***line added to each group

p+geom_point(size=5)+stat_smooth(method="lm", formula=y~poly(x,2))
Warning message:
Computation failed in `stat_smooth()`:
'degree' must be less than number of unique points
***no line added to any group

test <- structure(list(one = 1:20, two = c(1L, 4L, 9L, 16L, 25L, 36L,
49L, 64L, 81L, 100L, 121L, 144L, 169L, 196L, 225L, 256L, 289L,
324L, 361L, 400L), three = c("a", "a", "a", "a", "b", "b", "b",
"b", "c", "c", "c", "c", "c", "d", "d", "e", "e", "e", "e", "e"
)), class = "data.frame", row.names = c(NA, -20L))

My question:
Is it possible to add smoothing line just to the groups where it can be
added? I know that I could exclude "d" level from my data but I would
prefer
to keep them and add only smoothing lines where they could be computed.

Looks like there's a tryCatch around each panel, but not for each group
within panel. So this would work:

p + geom_point(size=2) + facet_wrap(~three) +
    stat_smooth(method="lm", formula=y~poly(x,2))

but one problematic group is enough to make a whole panel fail.

Other than rewriting StatSmooth$compute_panel to protect each per-group
call, a workaround could be to replace method="lm" by a safe wrapper, e.g.,:

plm <- function(formula, data, ...)
{
    ocall <- match.call(expand.dots = TRUE)
    ocall[[1]] <- quote(lm)
    fm <- try(eval(ocall, parent.frame()), silent = TRUE)
    if (inherits(fm, "try-error"))
    {
        ocall[[2]] <- y ~ x
        fm <- eval(ocall, parent.frame())
    }
    fm
}

p + geom_point(size=2) + stat_smooth(method=plm, formula=y~poly(x,2))

-Deepayan

Best regards
Petr
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ggplot stat smooth and poly

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