Question

I am using R to plot trying to conditionally change parts of an array
based on the columns of the array.

I have worked out the following steps:

x<-array(1,dim=c(4,4,3))
r<-x[,,1]
g<-x[,,2]
b<-x[,,3]

r1<-apply(r[,2:3],1:2,function(f){return(0)})
g1<-apply(g[,2:3],1:2,function(f){return(0)})
b1<-apply(b[,2:3],1:2,function(f){return(0)})

r3<-cbind(r[,1],r1,r[,4])
g3<-cbind(g[,1],g1,g[,4])
b3<-cbind(b[,1],b1,b[,4])

# Pass to pixmapRGB

This works, but as I am new to R, I was wondering if
there was a more efficient way to manipulate parts
of an array.

For example, does apply know which element it is working on?

The bigger picture is that I want to graph a time-series scatter
plot over many pages.

I would like to have a thumbnail in the corner of the page that is
a graph of the whole series. I would like to color a portion of
that thumbnail a different color to indicate what range the
current page is examining.

There is alot of data, so it is not feasible to redraw a new plot
for the thumbnail on every page.

What I have done is to first write the thumbnail plot out to a tiff file.
Then I read the tiff file back in, used getChannels from pixmap
to break the picture into arrays, and used the above code to change
some of the pixels based on column.
Finally I then print the image to a viewport using
pixmapRGB/pixmapGrob/grid.draw

It seems like alot of steps. I would be grateful for any pointers
that would help me make this more efficient.

Answer 1

Maybe I don’t understand your question, but if what you’re trying to do is just “change some pixels based on column,” why don’t you just use the basic array indexing to do that?

This will do the same thing you have posted:

x<-array(1,dim=c(4,4,3))
r<-x[,,1]
g<-x[,,2]
b<-x[,,3]
r[,2:3]=0
g[,2:3]=0
b[,2:3]=0

Is that helpful?