Re: [R] Scatterplot Showing All Points

From: Jim Lemon <jim_at_bitwrit.com.au>
Date: Tue, 18 Dec 2007 19:10:22 +1100

Wayne Aldo Gavioli wrote:
>
> Hello all,
>
>
> I'm trying to graph a scatterplot of a large (5,000 x,y coordinates) of data
> with the caveat that many of the data points overlap with each other (share the
> same x AND y coordinates). In using the usual "plot" command,
>
>
>

>>plot(education, xlab="etc", ylab="etc")

>
>
>
> it seems that the overlap of points is not shown in the graph. Namely, there
> are 5,000 points that should be plotted, as I mentioned above, but because so
> many of the points overlap with each other exactly, only about 50-60 points are
> actually plotted on the graph. Thus, there's no indication that Point A shares
> its coordinates with 200 other pieces of data and thus is very common while
> Point B doesn't share its coordinates with any other pieces of data and thus
> isn't common at all. Is there anyway to indicate the frequency of such points
> on such a graph? Should I be using a different command than "plot"?
>
Hi Wayne,
While this is not a really pretty picture, you can get a viewable plot with count.overplot if the first two elements of "education" are named "x" and "y" and they are the coordinates you want to plot. Otherwise, pass the x and y coordinates separately.

library(plotrix)
count.overplot(education,
  tol=c(diff(range(education$x))/10,
  diff(range(education$y))/10))

Jim



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