Using the try and try catch function on .WAV files - r

Question

Trying to cut a bunch of audio (.WAV) files into smaller samples in R. For this example, I'm using a loop to cut out 1 minute samples at 140 minutes.
For some files, the recording ends before 140 minutes due to an error in the recording device. When this occurs, an error appears -- and the loop stops. I'm trying to make it so the loop continues by using the try or tryCatch function however keep getting errors.
The code is as follows:
for(i in 1:length(AR_CD288)){
CUT_AR288_5 <- try({readWave(AR_CD288[i], from = 140, to = 141, units = "minutes")})
FILE.OUT_AR288_5<- sub("\\.wav$", "_140.wav", AR_CD288)
OUT.PATH_AR288_5 <- file.path("New files", basename(FILE.OUT_AR288_5))
writeWave(CUT_AR288_5, extensible=FALSE, filename = OUT.PATH_AR288_5[i])
}
I get the following two errors from the code:
Error in readBin(con, int, n = N, size = bytes, signed = (bytes != 1), :
invalid 'n' argument
Error in writeWave(CUT_AR288_5, extensible = FALSE, filename = OUT.PATH_AR288_5[i]) :
'object' needs to be of class 'Wave' or 'WaveMC
The loop still saves some samples into the "New files" directory, however, once the loop reaches a file <140 minutes, the loop stops.
I am very stuck! Any help would be greatly appreciated.
Cheers.

Answer 1

When I use try, I always do one (or both) of:
check the return value to see if it inherits "try-error", indicating that the command failed; or
add try(., silent = TRUE), indicating that I don't care if it succeeded (but this implies that I will not use its return value, either).
Try this:
for (i in seq_along(AR_CD288)) {
CUT_AR288_5 <- try({
readWave(AR_CD288[i], from = 140, to = 141, units = "minutes")
}, silent = TRUE)
if (!inherits(CUT_AR288_5, "try_error")) {
FILE.OUT_AR288_5 <- sub("\\.wav$", "_140.wav", AR_CD288)
OUT.PATH_AR288_5 <- file.path("New files", basename(FILE.OUT_AR288_5))
writeWave(CUT_AR288_5, extensible = FALSE, filename = OUT.PATH_AR288_5[i])
}
}
Three notes:
I changed 1:length(.) to seq_along(.); the latter is more resilient in an automated use when it is feasible that the vector might be length 0. For example, if AR_CD288 can ever be length 2, intuitively we expect 1:length(AR_CD288) to return nothing so that the for loop will not run; unfortunately, it resolves to 1:0 which returns a vector of length 2, which will often fail (based on whatever code is operating in the loop). The use of seq_along(.) will always return a vector of length 0 with an empty input, which is what we need. (Alternatively and equivalent, seq_len(length(AR_CD288)), though that's really what seq_along is intended to do.)
If you do not add silent=TRUE (or explicitly add silent=FALSE), then you will get an error message indicating that the command failed. Unfortunately, the error message may not indicate which i failed, so you may be left in the dark as far as fixing or removing the errant file. You may prefer to add an else to the if (inherits(.,"try-error")) clause so that you can provide a clearer error, such as
if (inherits(CUT_AR288_5, "try_error")) {
warning("'readWave' failed on ", sQuote(AR_CD288[i]), call. = FALSE)
} else {
FILE.OUT_AR288_5 <- sub("\\.wav$", "_140.wav", AR_CD288)
# ...
}
(noting that I put the "things worked" code in the else clause here ... I find it odd to do if (!...) {} else {}, seems like a double-negation :-).
The choice to wrap one function or the whole block depends on your needs: I tend to prefer to know exactly where things fail, so the will-possibly-fail functions are often individually wrapped with try so that I can react (or log/message) accordingly. If you don't need that resolution of error-detection, then you can certainly wrap the whole code-block in a sense:
for (i in seq_along(AR_CD288)) {
ret <- try({
CUT_AR288_5 <- readWave(AR_CD288[i], from = 140, to = 141, units = "minutes")
FILE.OUT_AR288_5 <- sub("\\.wav$", "_140.wav", AR_CD288)
OUT.PATH_AR288_5 <- file.path("New files", basename(FILE.OUT_AR288_5))
writeWave(CUT_AR288_5, extensible = FALSE, filename = OUT.PATH_AR288_5[i])
}, silent = TRUE)
if (inherits(ret, "try-error")) {
# do or log something
}
}