alternative to is null in R

Question

my R code ends up containing plethora of statements of the form   if   is null aVariable           do whatever      But this kind of statement is hard to read because it contains two negations  I would prefer something like     if  is defined aVariable            do whatever       Does a is defined type function that does the opposite of  is null exist standard in R   cheers  yannick

User · Answer

To handle undefined variables as well as nulls  you can use substitute with deparse   nullSafe  lt - function x      if   exists deparse substitute x       is null x         return NA      else       return x         nullSafe my nonexistent var

User · Answer

You may be better off working out what value type your function or code accepts  and asking for that   if  is integer aVariable       do whatever     This may be an improvement over isnull  because it provides type checking   On the other hand  it may reduce the genericity of your code   Alternatively  just make the function you want   is defined   function x  is null x

User · Answer

I have also seen    if length obj         do this if object has length     NULL has no length     I don t think it s great though  Because some vectors can be of length 0  character 0   logical 0   integer 0  and that might be treated as a NULL instead of an error

User · Answer

The shiny package provides the convenient functions validate   and need   for checking that variables are both available and valid  need   evaluates an expression  If the expression is not valid  then an error message is returned  If the expression is valid  NULL is returned  One can use this to check if a variable is valid  See  need for more information   I suggest defining a function like this   is valid  lt - function x      require shiny    is null need x  message   FALSE         This function is valid   will return FALSE if x is FALSE  NULL  NA  NaN  an empty string     an empty atomic vector  a vector containing only missing values  a logical vector containing only FALSE  or an object of class try-error  In all other cases  it returns TRUE   That means  need    and is valid    covers a really broad range of failure cases  Instead of writing   if   is null x   amp  amp   is na x   amp  amp   is nan x               one can write simply   if  is valid x               With the check for class try-error  it can even be used in conjunction with a try   block to silently catch errors   see https   csgillespie github io efficientR programming html communicating-with-the-user   bad   try 1    1   silent   TRUE  if  is valid bad

User · Answer

If it s just a matter of easy reading  you could always define your own function    is not null  lt - function x   is null x    So you can use it all along your program   is not null 3  is not null NULL

User · Answer

Ian put this in the comment  but I think it s a good answer   if  exists  aVariable        do whatever     note that the variable name is quoted

[r] alternative to "!is.null()" in R

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