does column exist?
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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