[R] plotting every ith data point?

[Jessi Brown]

Thanks for the ideas so far, Gabor and Phil.

I was hoping to find a solution that didn't depend on building another
data frame, but if that's the easiest way, I can certainly do it
through that route. At least your solutions involve fewer lines of
code than I had devised for extracting the desired rows (am still a
newbie at data manipulation with R!).

cheers, Jessi

On Wed, Feb 20, 2008 at 7:08 PM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> 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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