R help - Feb 2023 - sparseMatrix image not working in for loop

Hi all,

I have just encountered a weird behavior of image(sparseMatrix) when 
trying to output plots to files in a for loop.

A sample code is provided below at the end of this mail as well as in 
the attachment. In the code, calling image(sparseMatrix) works outside 
of a for loop - the image file is written. Calling 
image(as.matrix(sparseMatrix)) also works inside a for loop thus 
eliminating file access problem. However when using image(sparseMatrix) 
inside for loop, no image file is produced, nor is there any error message.

The execution environment is on 2 different distributions of Linux 
running R 3.6.3 and 4.2.1, Matrix library 1.2-18 and 1.5-3 respectively, 
and all showing the same behavior.

Can anyone point me a direction on where to look for?

Sincerely,

Shunran Zhang

--- Sample code ---

# Initialize dataset library(Matrix) set.seed(0) filler <- 
list(sample(1:1000,1000), sample(1:1000,1000), runif(1000,0,100)) 
sampledata <- sparseMatrix(i = filler[[1]], j = filler[[2]], x = 
filler[[3]], dims = c(1000,1000)) # Works: image on a sparse matrix 
outside for loop item <- "a"
png(paste("img/out_of_for_",item,".png",
sep = "", collapse = ""), width = 1000, height = 1000)
image(sampledata)
dev.off() remove(item) for(item in c("a")){ ?# Does not work: image on
a
sparse matrix inside for loop
?png(paste("img/in_for_img_",item,".png",
sep = "", collapse = ""), width = 1000, height = 1000) 
 ?image(sampledata) ?dev.off() ?# Works: image on a dense matrix inside 
for loop ?png(paste("img/in_for_hist_",item,".png", sep =
"", collapse =
""), width = 1000, height = 1000) ?image(as.matrix(sampledata)) 
 ?dev.off() }

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On Mon, 13 Feb 2023 13:08:18 +0900
Shunran Zhang <szhang at ngs.gen-info.osaka-u.ac.jp> wrote:
> In the code, calling image(sparseMatrix) works outside 
> of a for loop - the image file is written. Calling 
> image(as.matrix(sparseMatrix)) also works inside a for loop thus 
> eliminating file access problem. However when using
> image(sparseMatrix) inside for loop, no image file is produced, nor
> is there any error message.
image() methods for Matrix objects use lattice graphics: they
internally call levelplot(). Lattice graphics don't directly draw their
plots; instead, they return objects of class "trellis" whose
print.trellis method actually performs the drawing. (The same thing
happens with ggplot2 graphics.)

You can use plot(image(...)) or print(image(...)) to force the plot to
be rendered even when there's no auto-printing (such as when you're
inside a for loop).

-- 
Best regards,
Ivan