Re: [R] does column exist?

From: Spencer Graves <spencer.graves_at_pdf.com>
Date: Fri 20 May 2005 - 04:12:05 EST

          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@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@mmm.com
> Tel: (651) 733-6092
> Fax: (651) 736-3122
>
>
>
> Omar Lakkis
> <uofiowa@gmail.co
> m> To
> Sent by: r-help@stat.math.ethz.ch
> r-help-bounces@st cc
> at.math.ethz.ch
> Subject
> [R] does column exist?
> 05/19/2005 12:42
> PM
>
>
> Please respond to
> Omar Lakkis
> <uofiowa@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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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri May 20 04:23:58 2005

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