R / Rstudio : is there a watch function to continuously monitor some values? - r

Question

I have a lot of different operations running on quite a big dataframe. It starts to be a pain for maintenance, especially with some data being improperly formatted, and I'm looking at some options to make my life easier.
The problem is that at one point in the flow of operations NAs are introduced in several lines, including the id (certainly due to some bad subsetting). Now I cannot find the culprit easily because I have each time to str() it, or to view() it in Rstudio... This takes time and I already did it once without finding the bad operation...
So I'm curious if there is some package answering to this problem or a way to program something "daemon-like", to pop up a warning message when a specific value appears.
A while loop doesn't help, because it evaluates all the statements, and of course at one point the condition is not true and it doesn't print when it stops ...
while(nrow(df[is.na(df$id),]) > 0){
statements OK
breaking statement
other OK statements
}
I'll look for other options but I wanted to ask before...
EDIT : thanks for the useful comments, I'll definitely will look more into those functions. However I tried also to build myself a watch function (see my answer).

Answer 1

Ok, I guess I have finally built something quite like it :
This is a function to source a file line per line until a given condition is met :
watchIt <- function(file,watchexpression,startwatchline){
line <- 1
sourceList <- scan(file = "source_test.R", what="character", sep="\n", blank.lines.skip = FALSE)
maxLines <- length(sourceList)
while(startwatchline > line && maxLines >= line){
cat("l")
eval(parse(text=sourceList[line]))
line <- line+1
cat(line)
cat(" ")
}
while(eval(parse(text=watchexpression)) == FALSE && maxLines >= line){
cat(" L")
eval(parse(text=sourceList[line]))
line <- line+1
cat(line)
cat(" ")
}
if(maxLines <= line) {
cat("End of file reached without condition getting TRUE")
}
else{
cat("Condition evaluated to TRUE on line :")
cat(line)
cat("\n")
cat(sourceList[line])
}
}
So this is how I use it :
watchIt("source_test.R","nrow(df[is.na(df$id),]) > 0",10)
This puts "source_test.R" in a list, each line a new list item, and, starting from line 10, I test if the resultant dataframe as NAs in the id field. The execution stops either when the condition evaluates TRUE or when the end of the list items is reached.
Still I'm waiting for some other/better answers... Also, this is kind of my fourth function I managed to create in R, so I guess there might be ameliorations to be made to it...