Error in if while condition missing Value where TRUE FALSE needed

Question

I received this error message   Error in if  condition      missing value where TRUE FALSE needed   or  Error in while  condition      missing value where TRUE FALSE needed   What does it mean  and how do I prevent it

User · Answer

this works with  quot NA quot  not for NA comments   c  quot no quot   quot yes quot   quot NA quot     for  l in 1 length comments          if   is na comments l    print comments l       if  comments l      quot NA quot   print comments l

User · Answer

The evaluation of condition resulted in an NA   The if conditional must have either a TRUE or FALSE result     if  NA        Error in if  NA      missing value where TRUE FALSE needed   This can happen accidentally as the results of calculations   if TRUE  amp  amp  sqrt -1         Error in if  TRUE  amp  amp  sqrt -1       missing value where TRUE FALSE needed     To test whether an object is missing use is na x  rather than x    NA     See also the related errors   Error in if while  condition      argument is of length zero  Error in if while  condition    argument is not interpretable as logical  if  NULL        Error in if  NULL      argument is of length zero  if   not logical         Error  argument is not interpretable as logical  if  c TRUE  FALSE         Warning message     the condition has length  gt  1 and only the first element will be used

User · Answer

I ran into this when checking on a null or empty string  if  x    NULL    x            changed it to  if  is null x     x

[r] Error in if/while (condition) {: missing Value where TRUE/FALSE needed

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