fastest way to create xlsx with plots R - r

Question

I have list of data and list of plots which I want two write to xlsx file (each element to separate sheet). Example data:
require(ggplot2)
require(data.table)
n <- 10
N <- 100
dtList <- lapply(1:n, function(x) data.table(sample(1e6, N), 1:N))
names(dtList) <- 1:n
plots <- lapply(dtList, function(x) ggplot(x, aes(y = V1, x = V2)) + geom_line())
Currently I use openxlsx, but it is quite slow for multiple plots:
require(openxlsx)
wb <- createWorkbook()
modifyBaseFont(wb, fontSize = 10)
writeXlsx <- function(x, sName) {
addWorksheet(wb, sName, gridLines = FALSE)
writeData(wb, sName, x = x, xy = c(1, 1))
print(plots[[sName]])
insertPlot(wb, sName, width = 19, height = 9, dpi = 200, units = "cm",
startRow = 2, startCol = 5)
}
system.time(
sapply(seq_along(dtList), function(x) {
writeXlsx(dtList[[x]], names(dtList)[[x]])
})
) # ~ 17.00 sek
openXL(wb)
How could I increase speed of this? Is there a better package to accomplish this?

Answer 1

One options is to use simpler graphics. For example, changing plots to base graphics, like:
plots <- lapply(dtList, function(x) plot(x$V2, x$V1, type = 'l'))
reduces the xlsx creation time to ~0.72 seconds vs ~7.78 seconds (original code works now faster than before), that is around 10 times faster.
When ggplot graphics are needed, I modified insertPlot function to accept this type of object and save it to file without needing to print in R session (using ggsave):
insertggPlot <- function(wb, sheet, width = 6, height = 4, xy = NULL,
startRow = 1, startCol = 1, fileType = "png",
units = "in", dpi = 300, PLOT) {
od <- getOption("OutDec")
options(OutDec = ".")
on.exit(expr = options(OutDec = od), add = TRUE)
if (!"Workbook" %in% class(wb)) stop("First argument must be a Workbook.")
if (!is.null(xy)) {
startCol <- xy[[1]]
startRow <- xy[[2]]
}
fileType <- tolower(fileType)
units <- tolower(units)
if (fileType == "jpg") fileType = "jpeg"
if (!fileType %in% c("png", "jpeg", "tiff", "bmp"))
stop("Invalid file type.\nfileType must be one of: png, jpeg, tiff, bmp")
if (!units %in% c("cm", "in", "px"))
stop("Invalid units.\nunits must be one of: cm, in, px")
fileName <- tempfile(pattern = "figureImage",
fileext = paste0(".", fileType))
ggsave(plot = PLOT, filename = fileName, width = width, height = height,
units = units, dpi = dpi)
insertImage(wb = wb, sheet = sheet, file = fileName, width = width,
height = height, startRow = startRow, startCol = startCol,
units = units, dpi = dpi)
}
Using this, reduces time to ~2 sek.