Hi,
On Wed, Oct 5, 2011 at 1:44 PM, JeffND <zuofeng.shan...@nd.edu> wrote:
> Dear folks,
>
> I have a question about the image() function in R. I found the following
> link talking about this
> but the replies didn't help with my situations.
>
> http://r.789695.n4.nabble.com/question-on-image-function-td839275.html#a839276
In fact, that link states exactly what needs to be done, and why.
> To be simple, I will keep using the example in the above link.
>
> Suppose the data are like
>
> x y mcpvalue
> 0.4603578 0.6247629 1.001
> 0.4603715 0.6247788 1.001
> 0.4603852 0.6247948 1.001
> 0.4110561 0.5664841 0.995
>
> So we have four points with coordinates given by the four pairs of (x,y)
> values.
> Each point is associated with a mcpvalue.
> How do we use image() to plot "mcpvalue" as a two-dimensional plot?
> I hope that the points are positioned by the coordinates and the color of
> each point
> in that plot is changing with the value of mcpvalue.
We don't. image() is intended to plot data on a regular grid, and that's not a
regular grid. You need to use kriging or some other form of spatial
interpolation
to fit it to a regular grid before you can use image().
You can however use plot() with the col= argument to plot points at the
actual values of the coordinates, and to color them as desired.
testdata <- structure(list(x = c(0.4603578, 0.4603715, 0.4603852, 0.4110561
), y = c(0.6247629, 0.6247788, 0.6247948, 0.5664841), mcpvalue = c(1.001,
1.001, 1.001, 0.995)), .Names = c("x", "y", "mcpvalue"), class =
"data.frame", row.names = c(NA, -4L))
testdata.colors <- cut(testdata$mcpvalue, c(0, 1, 2))
testdata.colors <- rainbow(length(testdata.colors))[testdata.colors]
with(testdata, plot(x, y, col=testdata.colors))
Which is kind of useless in this case, but may work with your actual
data, which is why I
wrote it out so elaborately.
> Using image() does not work as the coordinates of the points
> are not ascending.
Exactly. So you can't use image().
--
Sarah Goslee
http://www.functionaldiversity.org
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