parse on left hand side of R assignment
At 11:57 AM 5/31/2003 -0500, Paul E. Johnson wrote:
I keep finding myself in a situation where I want to calculate a variable
name and then use it on the left hand side of an assignment. For example
iteration <- 1
varName <- paste("run",iteration,sep="")
myList$parse(text=varName) <- aColumn
I want to take some existing variable "aColumn" and use the name
"varName" name for it and put it into a list "myList". That use fails
with this error:
Error: couldn't find function "(<-"
I've tried many variations on the theme.
If I could do this with a data frame, I would be just as happy. Right now
I'm using a list rather than a data frame because not all columns are of
the same length. But I can work around that.
Dear Paul,
I don't think that assign() will work in this context, but I may be wrong.
One way to proceed is with eval() and parse(), assembling the command to be
executed as a text string; for example,
eval(parse(text=paste("myList$", varName, " <- aColumn", sep=""))), though
you do have to be careful about the environment in which the expression is
evaluated -- see the envir argument to eval.
I hope that this helps,
John
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox