Alternatively, you can use subset(), which supports the ":" operator
for the 'select' argument:
> cor(subset(iris, select = Sepal.Length:Petal.Length))
Sepal.Length Sepal.Width Petal.Length
Sepal.Length 1.0000000 -0.1175698 0.8717538
Sepal.Width -0.1175698 1.0000000 -0.4284401
Petal.Length 0.8717538 -0.4284401 1.0000000
which is equivalent to:
> cor(iris[, 1:3])
Sepal.Length Sepal.Width Petal.Length
Sepal.Length 1.0000000 -0.1175698 0.8717538
Sepal.Width -0.1175698 1.0000000 -0.4284401
Petal.Length 0.8717538 -0.4284401 1.0000000
So for the pollute data:
cor(subset(pollute, select = Pollution:Industry))
should work.
Note also that the 'select' argument to subset can take non-contiguous
column names:
# Skip 'Sepal.Width'
> cor(subset(iris, select = c(Sepal.Length, Petal.Length:Petal.Width)))
Sepal.Length Petal.Length Petal.Width
Sepal.Length 1.0000000 0.8717538 0.8179411
Petal.Length 0.8717538 1.0000000 0.9628654
Petal.Width 0.8179411 0.9628654 1.0000000
So you have the option of specifying, by name, multiple series of
contiguous and non-contiguous column names.
See ?subset
HTH,
Marc Schwartz
On Dec 5, 2009, at 10:43 AM, Ista Zahn wrote:
As baptiste noted, you can do
cor(pollute[ ,c("Pollution","Temp","Industry")]).
But
cor(pollute[,"Pollution":"Industry"])
will not work. For that you can do
cor
(pollute
[ ,which
(names(pollute)=="Pollution"):which(names(pollute)=="Industry")])
-Ista
On Sat, Dec 5, 2009 at 11:22 AM, John-Paul Ferguson
<ferguson_john-p...@gsb.stanford.edu> wrote:
I apologize for how basic a question this is. I am a Stata user who
has begun using R, and the syntax differences still trip me up. The
most basic questions, involving as they do general terms, can be the
hardest to find solutions for through search.
Assume for the moment that I have a dataset that contains seven
variables: Pollution, Temp, Industry, Population, Wind, Rain and
Wet.days. (This actual dataset is taken from Michael Crawley's
"Statistics: An Introduction Using R" and is available as
"pollute.txt" in
http://www.bio.ic.ac.uk/research/crawley/statistics/data/zipped.zip.)
Assume I have attached pollute. Then
cor(pollute)
will give me the correlation table for these seven variables. If I
would prefer only to see the correlations between, say, Pollution,
Temp and Industry, I can get that with
cor(pollute[,1:3])
or with
cor(pollute[1:3])
Similarly, I can see the correlations between Temp, Population and
Rain with
cor(pollute[,c(2,4,6)])
or with
cor(pollute[c(2,4,6)])
This is fine for a seven-variable dataset. When I have 250 variables,
though, I start to pale at looking up column indexes over and over. I
know from reading the list archives that I can extract the column
index of Industry, for example, by typing
which("Industry"==names(pollute))
but doing that before each command seems dire. Trained to using Stata
as I am, I am inclined to check the correlation of the first three or
the second, fourth and sixth columns by substituting the column names
for the column indexes--something like the following:
cor(pollute[Pollution:Industry])
cor(pollute[c(Temp,Population,Rain)])
These however throw errors.
I know that many commands in R are perfectly happy to take variable
names--the regression models, for example--but that some do not. And
so I ask you two general questions:
1. Is there a syntax for referring to variable names rather than
column indexes in situations like these?
2. Is there something that I should look for in a command's help file
that often indicates whether it can take column names rather than
indexes?
Again, apologies for asking something that has likely been asked
before. I would appreciate any suggestions that you have.
Best,
John-Paul Ferguson
Assistant Professor of Organizational Behavior
Stanford University Graduate School of Business
518 Memorial Way, K313
Stanford, CA 94305
______________________________________________
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.
______________________________________________
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.
