On Jun 21, 2011, at 9:57 AM, Ista Zahn wrote:
I would cation people not to use the -which strategy because entering
a value that doesn't exist as a column name returns a zero-column
data.frame, without so much as a warning. This can be a problem if you
don't know if a column exists but just want to make sure it doesn't,
or if you make a typo. Compare
head(mtcars[, -which(names(mtcars) == "make.sure.to.delete")])
to
head(mtcars[, setdiff(names(mtcars), "make.sure.to.delete")])
Excellent point, and also applies to the greppish strategies.
Although these do give the desired results:
# [which( ... != <target>)]
> head(mtcars[, which(names(mtcars) != "make.sure.to.delete")])
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
# Logical negation of grepl result
> head( mtcars[ , !grepl("^make.sure.to.delete$", names(mtcars) ) ] )
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
Best,
Ista
On Tue, Jun 21, 2011 at 12:22 AM, Joshua Wiley
<jwiley.ps...@gmail.com> wrote:
On Mon, Jun 20, 2011 at 8:55 PM, Erin Hodgess <erinm.hodg...@gmail.com
> wrote:
Too funny!
how about subset?
Sure, that is one option. Each of the following will also work. The
ones wrapped with c() can easily omit more than one at a time.
mtcars[, -which(names(mtcars) == "drat")]
mtcars[, names(mtcars) != "drat"]
mtcars[, !names(mtcars) %in% c("drat")]
mtcars[, -match(c("drat"), names(mtcars))]
On Mon, Jun 20, 2011 at 10:52 PM, Joshua Wiley <jwiley.ps...@gmail.com
> wrote:
Hi Erin,
See inline.
On Mon, Jun 20, 2011 at 8:45 PM, Erin Hodgess <erinm.hodg...@gmail.com
> wrote:
Dear R People:
I have a data frame, xm1, which has 12 rows and 4 columns.
If I put is xm1[,-4], I get all rows, and columns 1 - 3, which
is as
it should be.
Okay, so you know how to use the column number to omit columns.
Now, is there a way to use the names of the columns to omit
them, please?
You have all the pieces (the column names, and the knowledge that
you
can omit columns by their index).
Homework: find a way to return the column numbers given the
column names (hint).
Cheers,
Josh
Thanks so much in advance!
Sincerely,
Erin
--
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: erinm.hodg...@gmail.com
______________________________________________
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.
--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
--
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: erinm.hodg...@gmail.com
--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
______________________________________________
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.
--
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org
______________________________________________
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.
David Winsemius, MD
West Hartford, CT
______________________________________________
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.
