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.