[R] Simple column selection question- which and character lists

[Erik Iverson]

1) Don't call your data.frame "data".  I will call my "example" one "df".

2) If you want the columns NOT in names.species.bio.18, which is what you said, then the answer is: 

df[!names(df) %in% names.species.bio.18]

Best,
Erik 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of AllenL
Sent: Monday, August 31, 2009 11:40 AM
To: r-help at r-project.org
Subject: [R] Simple column selection question- which and character lists


Dear R-list,
Seems simple but have tried multiple approaches, no luck.

I have a list of column names:
>names.species.bio.18=c("Achimillb","Agrosmitb","Amorcaneb","Andrgerab","Ascltubeb","Elymcanab","Koelcrisb","Lespcapib","Liataspeb","Lupipereb","Monafistb","Panivirgb","Petapurpb","Poaprateb","Querellib","Quermacrb","Schiscopb","Sorgnutab")

I want to select the column numbers which correspond to these names in my
data frame:
>which(colnames(data)==names.species.bio.18)

Result:
+[1] 75 76
+Warning message:
+In cols == names.species.bio.18 :
+  longer object length is not a multiple of shorter object length

So I get the first two hits and then it trips an error message.

What is  >which doing? Why does it seem to have trouble with vectors of
characters? 
My goal is to output the column names/indices which correspond to the
columns NOT in the above list, but that is simple once I can find out what
they are.

Thanks!
-Allen

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