Message-ID: <428CD6F5.3070904@pdf.com>
Date: 2005-05-19T18:12:05Z
From: Spencer Graves
Subject: does column exist?
In-Reply-To: <OFFB688EFD.2F771D67-ON86257006.00621F35-86257006.00624612@mmm.com>
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
> r-help-bounces at st cc
> 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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