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

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

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

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

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

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

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

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

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