[R] Tying to underdressed the magic of lm redux

[Sorkin, John]

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 using gmail.com>
Sent: Wednesday, May 29, 2019 11:27 PM
To: Sorkin, John
Cc: r-help using 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 using som.umaryland.edu<mailto:jsorkin using 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 using gmail.com<mailto:bgunter.4567 using 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 using som.umaryland.edu<mailto:jsorkin using 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)

}




        [[alternative HTML version deleted]]

______________________________________________
R-help using r-project.org<mailto:R-help using r-project.org> mailing list -- To UNSUBSCRIBE and more, see
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.

	[[alternative HTML version deleted]]