[R] plot multiple data sets on same axis

[jim holtman]

Here is one way of doing it by splitting the data and plotting each
set in a different color:

# generate some test data
mydf <- data.frame(x=runif(200), y=rnorm(200),
dataset=sample(LETTERS[1:4], 200, TRUE))
# setup the plot are for the maximum of the data
plot(0, xlim=range(mydf$x), ylim=range(mydf$y), type='n', ylab="Y", xlab="X")
# split by 'dataset' and then plot each series; sort by 'x' first
mydf[] <- mydf[order(mydf$x),]
split.df <- split(mydf, mydf$dataset)
# loop through each set and plot with a different color
for (i in seq_along(split.df)){
    lines(split.df[[i]]$x, split.df[[i]]$y, col=i)
}


On Dec 30, 2007 5:11 PM, Scott Lamb <slamb at slamb.org> wrote:
> I'm new to R and struggling to reproduce graphs I've made with gnuplot.
> Example here:
>
>    http://www.slamb.org/tmp/one-active.png
>
> I have three different data sets plotted on the same axis. (I also have
> a number of samples for each X value which I displayed with quartiles
> rather than plotting every point; that will likely be the subject of my
> next question.)
>
> My attempts to do this in R: I've put the data into a frame with (x, y,
> dataset) columns; dataset is a categorical variable. I can get a coplot
> which sort of shows the information:
>
>    attach(myframe)
>    coplot(y ~ x | dataset)
>
> but not on the same axis with a legend. I'd like to start by getting
> that in a scatterplot form:
>
>    # XXX: datasets hardcoded in here...
>    # is split() supposed to do something similar to this?
>    # or how do I get a list of datasets to feed into subset?
>    myframe_a <- subset(myframe, dataset=='a')
>    myframe_b <- subset(myframe, dataset=='b')
>    ...
>
> and then I can apparently plot one and add points from others to it:
>
>    # XXX: more hardcoding...
>    attach(myframe_a)
>    plot(x, y, col='red')
>    detach(myframe_a)
>    attach(myframe_b)
>    points(x, y, col='blue')
>    detach(myframe_b)
>    ...
>    legend("topleft",
>           legend=c("a", "b", ...),
>           fill=c("red", "blue", ...))
>
> but there are several things I don't like about this solution:
>
> * there probably is an existing function which does this? I can't find it.
>
> * obviously I don't want to duplicate code for each dataset. I'd rather
> loop based on whatever datasets are in the frame, but I'm missing how to
> do that here.
>
> * points() appears to not alter xlim and ylim. Is there a convenient way
> to autodetermine them based on all the points?
>
> * I've hardcoded the colors. This is the sort of thing I'd rather leave
> to an expert. (I.e. someone who has looked at colorblindness studies and
> knows which colors are easiest to distinguish.)
>
> Any ideas?
>
> Cheers,
> Scott
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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