file.show and user input in a loop - r

Question

I have a dataframe data with information on tiffs, including one column txt describing the content of the tiff. Unfortunately, txt is not always correct and we need to correct them by hand. Therefore I want to loop over each row in data, show the tiff and ask for feedback, which is than put into data$txt.cor.
setwd(file.choose())
Some test tiffs (with nonsene inside, but to show the idea...):
txt <- sample(100:199, 5)
for (i in 1:length(txt)){
tiff(paste0(i, ".tif"))
plot(txt[i], ylim = c(100, 200))
dev.off()
}
and the dataframe:
pix.files <- list.files(getwd(), pattern = "*.tif", full.names = TRUE)
pix.file.info <- file.info(pix.files)
data <- cbind(txt, pix.file.info)
data$file <- row.names(pix.file.info)
data$txt.cor <- ""
data$txt[5] <- 200 # wrong one
My feedback function (error handling stripped):
read.number <- function(){
n <- readline(prompt = "Enter the value: ")
n <- as.character(n) #Yes, character. Sometimes we have alphanumerical data or leading zeros
}
Now the loop, for which help would be very much appreciated:
for (i in nrow(data)){
file.show(data[i, "file"]) # show the image file
data[i, "txt.cor"] <- read.number() # aks for the feedback and put it back into the dataframe
}
In my very first attempts I was thinking of the plot.lm idea, where you go through the diagnostic plots after pressing return. I suspect that plot and tiffs are not big friends. file.show turned out to be easier. But now I am having a hard time with that loop...

Answer 1

Your problem is that you don't loop over the data, you only evaluate the last row. Simply write 1:nrow(data)to iterate over all rows.
To display your tiff images in R you can use the package rtiff:
library(rtiff)
for (i in 1:nrow(data)){
tif <- readTiff(data[i,"file"]) # read in the tiff data
plot(tif) # plot the image
data[i, "txt.cor"] <- read.number() # aks for the feedback and put it back into the dataframe
}