[R] does column exist?

[Spencer Graves]

	  It depends on what Omar means by "a column named X".  Consider the 
following:

 > tstDF <- data.frame(aa=1, bb=2)
 > tstDF$a
[1] 1
 > is.null(tstDF$a)
[1] FALSE
 > is.na(match("a", names(tstDF)))
[1] TRUE

	  Does tstDF have a column named "a"?  It has a column named "aa", 
which is accessed by tstDF$a;  is.null(tstDF$a) correctly identifies its 
presence, while is.na(match("a", names(tstDF))) correctly says that "a" 
is not the official name of any column of tstDF.

	  spencer graves

apjaworski at mmm.com wrote:

> 
> 
> 
> 
> There may be a simpler way, but this
> 
> is.na(match("X", names(df)))
> 
> should return TRUE if the column name exists and FALSE otherwise.
> 
> Cheers,
> 
> Andy
> 
> __________________________________
> Andy Jaworski
> 518-1-01
> Process Laboratory
> 3M Corporate Research Laboratory
> -----
> E-mail: apjaworski at mmm.com
> Tel:  (651) 733-6092
> Fax:  (651) 736-3122
> 
> 
>                                                                            
>              Omar Lakkis                                                   
>              <uofiowa at gmail.co                                             
>              m>                                                         To 
>              Sent by:                  r-help at stat.math.ethz.ch            
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>              at.math.ethz.ch                                               
>                                                                    Subject 
>                                        [R] does column exist?              
>              05/19/2005 12:42                                              
>              PM                                                            
>                                                                            
>                                                                            
>              Please respond to                                             
>                 Omar Lakkis                                                
>              <uofiowa at gmail.co                                             
>                     m>                                                     
>                                                                            
>                                                                            
> 
> 
> 
> 
> How do I test if a data.frame has a column named X?
> exists(o) checks if the object exists or not, I want to test if a
> data.frame object (df) has a column names(X), something like:
> exists(df$X)
> 
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