Tying to underdressed the magic of lm redux
PS: lm records a copy of the call in its result, but has no other use for any name the data frame may have had.
On Sun, 2 Jun 2019 at 14:45, Richard O'Keefe <raoknz at gmail.com> wrote:
You can find the names of the columns of a dataframe using
colnames(my.df)
A dataframe is a value just as much as a number is, and as such,
doesn't _have_ a name. However, when you call a function in R,
the arguments are not evaluated, and their forms can be recovered,
just as "plot" does. In fact, looking at plot to see how it does
that is a good idea.
demo <- function (df) {
list(name = deparse(substitute(df)), cols = colnames(df))
}
my.df <- data.frame(x = c(1,2), y = c(3,4))
demo(my.df)
$name
[1] "my.df"
$cols
[1] "x" "y"
On Sun, 2 Jun 2019 at 13:43, Sorkin, John <jsorkin at som.umaryland.edu>
wrote:
Colleagues,
Despite Bert having tried to help me, I am still unable to perform a
simple act with a function. I want to pass the names of the columns of a
dataframe along with the name of the dataframe, and use the parameters to
allow the function to access the dataframe and modify its contents.
I apologize multiple postings regarding this question, but it is a
fundamental concept that one who wants to program in R needs to know.
Thank you,
John
# Create a toy dataframe.
df <- data.frame(a=c(1:20),b=(20:39))
df
# Set up a function that will access the first and second columns of the
# data frame, print the columns of the dataframe and add the columns
demo <- function(first,second,df)
{
# None of the following work
print(df[,all.vars(first)])
print(df[,first])
print(df[,"first"])
print(df[,all.vars(second)])
print(df[,second])
print(df[,"second"])
df[,"sum"] <- print(df[,first])+print(df[,second])
}
demo(a,b, df)
John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and
Geriatric Medicine
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)
________________________________
From: Bert Gunter <bgunter.4567 at gmail.com>
Sent: Wednesday, May 29, 2019 11:27 PM
To: Sorkin, John
Cc: r-help at r-project.org
Subject: Re: [R] Tying to underdressed the magic of lm redux
Depends on how you want to specify variables. You are not clear (to me)
on this. But, for instance:
demo <- function(form,df)
{
av <- all.vars(form)
df[,av]
}
demo(~a+b, df)
demo(a~b,df)
?all.vars, ?all.names for details
Bert Gunter
On Wed, May 29, 2019 at 7:33 PM Sorkin, John <jsorkin at som.umaryland.edu
<mailto:jsorkin at som.umaryland.edu>> wrote:
Bert,
Thank you for your reply. You are correct that your code will print the
contents of the data frame. While it works, it is not as elegant as the lm
function. One does not have to pass the independent and dependent variables
to lm In parentheses.
Fit1<-lm(y~x,data=mydata)
None of the parameters to lm are passed in quotation marks. Somehow,
using deparse(substitute()) and other magic lm is able to get the data in
the dataframe mydata. I want to be able to do the same magic in functions I
write; pass a dataframe and column names, all without quotation marks and
be able to write code that will provide access to the columns of the
dataframe without having to pass the column names in quotation marks.
Thank you,
John
John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and
Geriatric Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-711<tel:410-605-7119>9
(Fax) 410-605-7913<tel:410-605-7913> (Please call phone number above
prior to faxing)
On May 29, 2019, at 9:59 PM, Bert Gunter <bgunter.4567 at gmail.com<mailto:
bgunter.4567 at gmail.com>> wrote:
Basically, huh?
df <- data.frame(a = 1:3, b = letters[1:3])
nm <- names(df)
print(df[,nm[1]])
[1] 1 2 3
print(df[,nm[2]])
[1] a b c
Levels: a b c
This can be done within a function, of course:
demo <- function(df, colnames){
+ print(df[,colnames])
+ }
demo(df,c("a","b"))
a b
1 1 a
2 2 b
3 3 c
Am I missing something? (Apologies, if so).
Bert Gunter
On Wed, May 29, 2019 at 6:40 PM Sorkin, John <jsorkin at som.umaryland.edu
<mailto:jsorkin at som.umaryland.edu>> wrote:
Thanks to several kind people, I understand how to use
deparse(substitute(paramter)) to get as text strings the arguments passed
to an R function. What I still can't do is put the text strings recovered
by deparse(substitute(parameter)) back together to get the columns of a
dataframe passed to the function. What I want to do is pass a column name
to a function along with the name of the dataframe and then, within the
function access the column of the dataframe.
I want the function below to print the columns of the dataframe testdata,
i.e. testdata[,"FSG"] and testdata[,"GCM"]. I have tried several ways to
tell the function to print the columns; none of them work.
I thank everyone who has helped in the past, and those people who will
help me now!
John
testdata <- structure(list(FSG = c(271L, 288L, 269L, 297L, 311L, 217L,
235L,
172L, 201L, 162L), CGM = c(205L, 273L,
226L, 235L, 311L, 201L,
203L, 155L, 182L, 163L)), row.names =
c(NA, 10L), class = "data.frame")
cat("This is the data frame")
class(testdata)
testdata
BAPlot <- function(first,second,indata){
# these lines of code work
col1 <- deparse(substitute(first))
col2 <- deparse(substitute(second))
thedata <- deparse(substitute(third))
print(col1)
print(col2)
print(thedata)
cat("This gets the data, but not as a dataframe\n")
zoop<-paste(indata)
print(zoop)
cat("End This gets the data, but not as a dataframe\n")
# these lines do not work
print(indata[,first])
print(indata[,"first"])
print(thedata[,col1])
paste(zoop[,paste(first)])
paste(zoop[,first])
zap<-paste(first)
print(zap)
}
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R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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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.