Filtering a data frame using a string for colum header

Hi Tony,

I "GUESS" my.df[-"DrHorrible"] does not tell R which column "NUMBER" 

like to remove.
As we know, we could use my.df[-4] and it exactly tells R which column 

remvoer from your data.

 > my.df[-4]

  Angel Buffy Firefly
1     7     8       9
2     8     9       9
3     6     4      10
4     9     9      10
5    10    10      10


I may be not right. 

-"DrHorrible"

Chunhao

Date: Sun, 22 Feb 2009 14:48:10 -0800
From: tony.breyal at googlemail.com
To: r-help at r-project.org
Subject: [R] Filtering a data frame using a string for colum header

Hi all,

I was just radomly playing with R and got the following error when
trying to filter a data frame using a string:

Angel <- c(7,8,6,9,10)
Buffy <- c(8,9,4,9,10)
Firefly <- c(9,9,10,10,10)
DrHorrible <- c(10,9,9,10,10)
my.df <- data.frame(Angel, Buffy, Firefly, DrHorrible)
my.df["DrHorrible"]

DrHorrible
1 10
2 9
3 9
4 10
5 10

my.df[-"DrHorrible"]

Error in -"DrHorrible" : invalid argument to unary operator

I know how to work around this problem quite easily, I'm just curious
as to why the my.df[-"DrHorrible] statement didn't work?

Cheers,
Tony

OS = win XP

sessionInfo()

R version 2.8.1 (2008-12-22)
i386-pc-mingw32

locale:
LC_COLLATE=English_United Kingdom.1252;LC_CTYPE=English_United 

1252;LC_MONETARY=English_United Kingdom.
1252;LC_NUMERIC=C;LC_TIME=English_United Kingdom.1252

attached base packages:
[1] stats graphics grDevices utils datasets methods
base