[R] plotting every ith data point?

[Gabor Grothendieck]

Try this:

ix <- seq(1, nrow(example.df), 5)
with(example.df[ix,], {
   plot(DSR1 ~ StartDate, type = "b", ylim = c(0.3, 0.9))
   points(DSR2 ~ StartDate, type = "b", pch = 3)
})


On Wed, Feb 20, 2008 at 6:57 PM, Jessi Brown <jessilbrown at gmail.com> wrote:
> Hello, fellow R enthusiasts.
>
> Ok, I've been racking my brain about this small issue, and between
> searching the help archives and reading through the plot-related
> documentation, I can't figure out how to achieve my desired endpoint
> without some ugly, brute force coding.
>
> What I would like to do is make a plot in which only a subset of my
> data are plotted, but in regular intervals, such as every 5th point
> along the sequence. Is anyone aware of a built-in function in plot or
> a related graphing family that can do this, or alternatively, a simple
> way to extract the desired rows from my original dataframe? I want to
> do this because I want to plot multiple series of points with their
> confidence intervals (arrows), and even if I specify type="b," the
> output ends up looking like just a series of crowded points.
>
> For example, if you try making the plot below, you will see how
> crowded two lines look without error bars:
>
> > example.df<-data.frame(StartDate=(94:157), DSR1=seq(0.4, 0.8, length.out=64), DSR2=seq(0.3, 0.9, length.out=64))
> > plot(example.df$StartDate, example.df$DSR1, type="b", ylim=c(0.3,0.9))
> > points(example.df$StartDate, example.df$DSR2, type="b", pch=3)
>
> Any ideas for an elegant solution to my dilemma?
>
> Thanks in advance for any help.
>
> cheers, Jessi Brown
>
> Ph.D. student
> Program in Ecology, Evolution, and Conservation Biology
> University of Nevada, Reno
>
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