Re: [R] Drop column from a data frame
On Dec 26, 2010, at 8:22 PM, John Sorkin wrote:
I am trying to drop a column of a data frame. The code below
attempts to drop a numeric column (which does not work but gives no
error or warning) and a factor column (which does not work but gives
an error).
I would appreciate someone telling me why my code does not work, and
suggesting code that will work.
You are misusing the syntax of the "[" operation. When using negative
indices you can only use numeric or logical values :
?"["
Character indices always need to be "positive".
dfxyz[ , -2] # works
dfxyz[ , c(T,F,T)] # works
> dfxyz[ , -"y"]
Error in -"y" : invalid argument to unary operator
This next mechanism also works and us especially useful on dataframes
with lots of columns:
dfxyz[ , -grep("y", names(dfxyz))]
But you need to be careful to make sure you know which columns will
match and its good practice to test the grepping expression first:
> grep("y", names(dfxyz))
[1] 2
If you only wanted to remove "y" and not "y2" you would need to add
qualifiers to the pattern.
Thanks,
John
rm(dfxyz,dfxz,dfxy)
# create the data frame.
dfxyz <- data.frame(x=1:10,y=11:20,z=factor(c(rep(0,5),rep(1,5
dfxyz
names(dfxyz)
# try to drop y column
# does not work, does not produce error message
dfxz <- dfxyz[,-(dfxyz$y)]
Well, dfxyz$y does evaluate to a numeric vector with values 11:20 and
there were no columns in that range. So it behaved as documented. You
asked for the dataframe without some non-existent (numbered) columns
and it obliged.
dfxz
# try to drop z column
# does not work, produces error message:
# In Ops.factor(df$z) : - not meaningful for factors
dfxy <- dfxyz[,-dfxyz$z]
Right, you cannot subtract (or negate) factors.
As Phil suggests, subset()-ting is often safer.
--
David.
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Re: [R] Drop column from a data frame
John -
You can use a syntax similar to what you've tried with
the select= argument of the subset function:
subset(dfxyz,select=-y)
x z
1 1 0
2 2 0
. . .
subset(dfxyz,select=-z)
x y
1 1 11
2 2 12
. . .
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spec...@stat.berkeley.edu
On Sun, 26 Dec 2010, John Sorkin wrote:
I am trying to drop a column of a data frame. The code below attempts to drop a
numeric column (which does not work but gives no error or warning) and a factor
column (which does not work but gives an error).
I would appreciate someone telling me why my code does not work, and suggesting
code that will work.
Thanks,
John
rm(dfxyz,dfxz,dfxy)
# create the data frame.
dfxyz <- data.frame(x=1:10,y=11:20,z=factor(c(rep(0,5),rep(1,5
dfxyz
names(dfxyz)
# try to drop y column
# does not work, does not produce error message
dfxz <- dfxyz[,-(dfxyz$y)]
dfxz
# try to drop z column
# does not work, produces error message:
# In Ops.factor(df$z) : - not meaningful for factors
dfxy <- dfxyz[,-dfxyz$z]
dfxy
John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)
Confidentiality Statement:
This email message, including any attachments, is for th...{{dropped:6}}
__
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] Drop column from a data frame
assign NULL to the column:
> dfxyz <- data.frame(x=1:10,y=11:20,z=factor(c(rep(0,5),rep(1,5
> dfxyz
x y z
1 1 11 0
2 2 12 0
3 3 13 0
4 4 14 0
5 5 15 0
6 6 16 1
7 7 17 1
8 8 18 1
9 9 19 1
10 10 20 1
> dfxyz$y <- NULL
> dfxyz
x z
1 1 0
2 2 0
3 3 0
4 4 0
5 5 0
6 6 1
7 7 1
8 8 1
9 9 1
10 10 1
>
On Sun, Dec 26, 2010 at 8:22 PM, John Sorkin
wrote:
> I am trying to drop a column of a data frame. The code below attempts to drop
> a numeric column (which does not work but gives no error or warning) and a
> factor column (which does not work but gives an error).
> I would appreciate someone telling me why my code does not work, and
> suggesting code that will work.
> Thanks,
> John
>
> rm(dfxyz,dfxz,dfxy)
>
> # create the data frame.
> dfxyz <- data.frame(x=1:10,y=11:20,z=factor(c(rep(0,5),rep(1,5
> dfxyz
>
> names(dfxyz)
>
> # try to drop y column
> # does not work, does not produce error message
> dfxz <- dfxyz[,-(dfxyz$y)]
> dfxz
>
> # try to drop z column
> # does not work, produces error message:
> # In Ops.factor(df$z) : - not meaningful for factors
> dfxy <- dfxyz[,-dfxyz$z]
> dfxy
>
>
>
> John David Sorkin M.D., Ph.D.
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
> Confidentiality Statement:
> This email message, including any attachments, is for ...{{dropped:17}}
__
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
[R] Drop column from a data frame
I am trying to drop a column of a data frame. The code below attempts to drop a
numeric column (which does not work but gives no error or warning) and a factor
column (which does not work but gives an error).
I would appreciate someone telling me why my code does not work, and suggesting
code that will work.
Thanks,
John
rm(dfxyz,dfxz,dfxy)
# create the data frame.
dfxyz <- data.frame(x=1:10,y=11:20,z=factor(c(rep(0,5),rep(1,5
dfxyz
names(dfxyz)
# try to drop y column
# does not work, does not produce error message
dfxz <- dfxyz[,-(dfxyz$y)]
dfxz
# try to drop z column
# does not work, produces error message:
# In Ops.factor(df$z) : - not meaningful for factors
dfxy <- dfxyz[,-dfxyz$z]
dfxy
John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)
Confidentiality Statement:
This email message, including any attachments, is for th...{{dropped:6}}
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
