R - plotting thumbnails (that are in a list) on a scatterplot

问题

I'd like to plot a set of thumbnail images as points on a scatterplot. I've started with the answer code located here but they repeat the same thumbnail throughout the plot, whereas I have a list of images.

xy <- data.frame(x=runif(337, 0, 100), y=runif(337, 0, 100))
imgfiles <- list.files(getwd(),pattern="*-scaled.png")
img <- lapply( imgfiles,function(x) readPNG(x) )

thumbnails <- function(x, y, images, width = 0.1*diff(range(x)), 
                       height = 0.1*diff(range(y))){

        images <- replicate(length(x), images, simplify=FALSE)
        stopifnot(length(x) == length(y))

        for (ii in seq_along(x)){
                rasterImage(images[[ii]], xleft=x[ii] - 0.5*width,
                            ybottom= y[ii] - 0.5*height,
                            xright=x[ii] + 0.5*width, 
                            ytop= y[ii] + 0.5*height, interpolate=FALSE)
        }
}

plot(xy, t="n")
thumbnails(xy[,1], xy[,2], img[[11]])        # this works but the same image is repeated

I've tried wrapping thumbnail() into a loop but the plot comes out empty

for (n in length(img)){
        thumbnails(xy[n,1], xy[n,2], img[[n]])        
}

How do I do this? I'm not understanding how to reference the images within the list, or whether i should change them to a different data structure.

回答1:

I just had to get rid of this line in thumbnails()

images <- replicate(length(x), images, simplify=FALSE)

It was replicating the sample image given in the original answer. There's no need for a loop after.

来源：https://stackoverflow.com/questions/37150889/r-plotting-thumbnails-that-are-in-a-list-on-a-scatterplot