R - argument is of length zero in if statement

Question

I am having a little problem with R and I am not sure why. It is telling me that this line: if(temp > data[[k]][[k2]]) { is of argument length 0. Here is the block which is not that big:

for(k in 1:length(data)) {        temp <- 0       for(k2 in 3:length(data[[k]])) {            print(data[[k]][[k2]])            if(temp > data[[k]][[k2]]) {                 temp <- data[[k]][[k2]]             }             fMax[k] <- temp            k2 <- k2 + 1       }  k <- k + 1  } 

example of what is in data[[k]][[k2]]:

[1] "3050" [1] "3051" [1] "3054" [1] "3054" [1] "3052" [1] "3053" [1] "3059" [1] "3059" [1] "3057" [1] "3060" [1] "3063" [1] "3060" [1] "3068" [1] "3067" [1] "3079" [1] "3085" [1] "3094" [1] "3107" [1] "3121" [1] "3135" [1] "3147" [1] "3161" [1] "3200" [1] "3237" [1] "3264" [1] "3274" [1] "3284" [1] "3289" [1] "3292" [1] "3300" [1] "3301" [1] "3303" [1] "3306" [1] "3310" [1] "3312" [1] "3313" [1] "3319" [1] "3314" [1] "3318" [1] "3318" [1] "3320" [1] "3322" [1] "3322" [1] "3322" [1] "3328" [1] "3332" [1] "3338" [1] "3350" [1] "3358" [1] "3378" [1] "3395" [1] "3402" [1] "3875" [1] "3950" [1] "3988" [1] "4018" [1] "4039" [1] "4048" [1] "4057" [1] "4062" [1] "4067" [1] "4076" [1] "4082" [1] "4085" [1] "4092" [1] "4098" [1] "4099" [1] "4101" [1] "4107" [1] "4119" [1] "4139" [1] "4164" [1] "4231" [1] "4347" [1] "4559" 

Thanks - Sam

Answer 1

"argument is of length zero" is a very specific problem that comes from one of my least-liked elements of R. Let me demonstrate the problem:

> FALSE == "turnip" [1] FALSE > TRUE == "turnip" [1] FALSE > NA == "turnip" [1] NA > NULL == "turnip" logical(0) 

As you can see, comparisons to a NULL not only don't produce a boolean value, they don't produce a value at all - and control flows tend to expect that a check will produce some kind of output. When they produce a zero-length output... "argument is of length zero".

(I have a very long rant about why this infuriates me so much. It can wait.)

So, my question; what's the output of sum(is.null(data[[k]]))? If it's not 0, you have NULL values embedded in your dataset and will need to either remove the relevant rows, or change the check to

if(!is.null(data[[k]][[k2]]) & temp > data[[k]][[k2]]){     #do stuff } 

Hopefully that helps; it's hard to tell without the entire dataset. If it doesn't help, and the problem is not a NULL value getting in somewhere, I'm afraid I have no idea.