On 26/09/2008, at 7:51 AM, kerfuffle wrote:
hi folks,
Bit of a newbie, but I've spent a fair bit of time looking for an
answer on
this, with no joy. Can anyone help me?
Dataset: A single column of values in a csv file (eg. 52, 53, 54,
85, etc)
Goal: In Minitab, you have what they call a dot plot. It's a
histogram,
where a single dot represents a set of identical values (eg. 57,
57, 57
would be one dot). Multiple dots are stacked on top of each other
(as if
gravity was affecting them). The advantage is that outliers are
very visible
(since a single 155 still gets a single dot). The net effect is a
rug plot,
but in the main portion of the plot, not just on the axis.
Tried: I've played with dotchart and dotchart2 with no joy (eg.
dotchart(nc$bac) (where nc is the dataset and bac is the column
header).
They do provide multiple dots (so that ten values of 57 are given 3
dots)
but these overlap and aren't arranged in a logical way. Sometimes
a single
dot has a large y-value, sometimes it isn't. As a result of this
non-gravitational effect, it doesn't look like a histogram at all.
It's
also strange that the background of the plot is stripy. This
implies I'm
doing something very wrong, but don't know what. I had a look at
the plot
galleries, and didn't see anything else that looked like what I wanted
(except the rug plots).
Here's something that will do at least roughly what you want. The
fundamentals of this function were written for me by Barry Rowlingson.
(Thanks Baz!)
dotplot.mtb <- function (x, xlim = NULL, main = NULL, xlab = NULL,
pch = 19,
hist = FALSE, yaxis = FALSE)
{
if (is.null(xlim))
xlim <- range(pretty(range(x)))
if (is.null(main))
main <- ""
if (is.null(xlab))
xlab <- ""
x <- sort(x)
w <- table(x)
mw <- max(w)
w <- unlist(lapply(w, function(n) {
1:n
}))
Nmax <- floor(par()$pin[2]/strheight("o", units = "inches"))
if (mw <= Nmax & !hist) {
plot(range(x, na.rm = TRUE), c(0, 1), type = "n", xlab = "",
ylab = "", xlim = xlim, main = main, axes = FALSE)
par(usr = c(par()$usr[1:2], -Nmax/2, Nmax/2))
y <- strheight("o") * w
points(x, y, pch = pch)
axis(side = 1, pos = 0)
if (yaxis) {
a <- 0
b <- round(Nmax/10)
at <- seq(a, by = b, length = 10)
axis(side = 2, at = at)
}
}
else {
if (hist)
plot(x, w, type = "h", xlab = "", ylab = "", xlim = xlim,
ylim = c(-mw - 1, mw + 1), main = main, axes = FALSE)
else plot(x, w, pch = pch, xlab = "", ylab = "", xlim = xlim,
ylim = c(-mw - 1, mw + 1), main = main, axes = FALSE)
axis(side = 1, pos = -0.02 * mw)
if (yaxis) {
a <- 0
b <- max(1, round(mw/10))
at <- seq(a, by = b, length = 10)
axis(side = 2, at = at)
}
}
}
cheers,
Rolf Turner
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