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  gt  data  k    k2      is of argument length 0  Here is the block which is not that big     for k in 1 length data            temp  lt - 0       for k2 in 3 length data  k                  print data  k    k2               if temp  gt  data  k    k2                      temp  lt - data  k    k2                             fMax k   lt - temp            k2  lt - k2   1          k  lt - 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

User · Answer

I spent an entire day bashing my head against this, the solution turned out to be simple..

R isn't zero-index.

Every programming language that I've used before has it's data start at 0, R starts at 1. The result is an off-by-one error but in the opposite direction of the usual. going out of bounds on a data structure returns null and comparing null in an if statement gives the argument is of length zero error. The confusion started because the dataset doesn't contain any null, and starting at position [0] like any other pgramming language turned out to be out of bounds.

Perhaps starting at 1 makes more sense to people with no programming experience (the target market for R?) but for a programmer is a real head scratcher if you're unaware of this.

User · Answer

You can use isTRUE for such cases  isTRUE is the same as   is logical x   amp  amp  length x     1  amp  amp   is na x   amp  amp  x    If you use shiny there you could use isTruthy which covers the following cases    FALSE NULL    An empty atomic vector An atomic vector that contains only missing values A logical vector that contains all FALSE or missing values An object of class  try-error  A value that represents an unclicked actionButton

User · Answer

The same error message results not only for null but also for e g  factor 0   In this case  the query must be if length element   gt  0  amp  otherCondition  or better check both cases with if  is null element   amp  length element   gt  0  amp  otherCondition

User · Answer

The simplest solution to the problem is to change your for loop statement   Instead of using       for  i in   0   n    Use       for  i in   1   n

User · Answer

The argument is of length zero takes places when you get an output as an integer of length 0 and not a NULL output i e   integer 0    You can further verify my point by finding the class of your output-  gt class output   integer

User · Answer

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    gt  FALSE     turnip   1  FALSE  gt  TRUE     turnip   1  FALSE  gt  NA     turnip   1  NA  gt  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     amp  temp  gt  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

[r] R - argument is of length zero in if statement

Examples related to r