(Forgot to copy the list.)
Begin forwarded message:
From: David Winsemius <dwinsem...@comcast.net>
Date: July 28, 2010 7:44:38 AM EDT
To: Tony <lul...@gmail.com>
Subject: Re: [R] How to point a column of dataframe by a "character"
On Jul 28, 2010, at 5:35 AM, Tony wrote:
Hello,
Here is a dilemma I am having for a long time. But, I couldn't
figure it
out.
I have an vector of Y and a data frame named "data",which contains
all Xs. I
tried to be more efficient in fitting a simple linear regression
with each
X.
Firstly,
for (i in 1:(dim(data)[2])){
model<-lm(Y~data[,i])
You could try instead:
model1 <- lm(Y ~ . , data=data[ , i, drop=FALSE])
I added the drop=FALSE to prevent a single column from being converted
to a nameless vector.
> testdf <- data.frame(testcol=letters[1:10], stringsAsFactors=FALSE)
> testdf[,1]
[1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
> testdf[,1, drop=FALSE]
testcol
1 a
2 b
3 c
4 d
5 e
6 f
7 g
8 h
9 i
10 j
BTW, "data" as the name for an object is a bad idea. As seen in the
line above, it means you brain needs to do extra work to keep straight
the fact that data is now the name for two things, the object and the
parameter. It could get even more complicated if you used the "data"
function. Notice that I even numbered the model. I thought the name
"model" was too non-specific.
David.
# this is not what I want since the name of coefficient will be
data[,i]
# I need coefficient name to be the name for each variable
# for instance:
# Coefficients:
# (Intercept) data[, 1]
# 24.2780 -0.3381
}
Second try!
I first create a vector of characters (Xs) that contains possible
names of
X. This vector is exactly the same as colnames of X.
#my Xs
Xs<-c("a","b","c")
for (i in length(Xs)){
model<-lm(Y~data[,Xs[i]])
# Again, not what I want
# Coefficients:
# (Intercept) data[, Xs[1]]
# 24.2780 -0.3381
}
Thus, how can I solve this dilemma?
I think about trying to find a function that can map the name of
variable to
values of that variable. That is, I first attach the data. I can
type a to
pull out values of data[,"a"] (a vector of numeric) directly.
However, using
Xs[1] will give me only "character" - "a". Thus, is there any
function that
allow me to pull values of dadta[,"a"] , eg, some_function(Xs[1])
give me
values of data[,"a"]
Any help is appreciated.
Tony
David Winsemius, MD
West Hartford, CT
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