Using assign with mapply
On Dec 6, 2013, at 11:27 AM, Julio Sergio Santana wrote:
I have a data frame whose first colum contains the names of the variables
and whose second colum contains the values to assign to them:
: kkk <- data.frame(vars=c("var1", "var2", "var3"),
vals=c(10, 20, 30), stringsAsFactors=F)
If I do
: assign(kkk$vars[1], kkk$vals[1])
it works
: var1
[1] 10
However, if I try with mapply this is what I get:
: mapply(assign, kkk$vars, kkk$vals)
var1 var2 var3
10 20 30
: var2
Error: object 'var2' not found
Maybe I have not undestand how mapply and assign work. Do you have
any comments?
I think you will find that the value returned from the mapply call was a three element list with the desired names and values ... except you then gave that enclosing list no name and it will be garbage-collected. If you want to have 'assign' do its magic into the global environment, then you need to supply 'mapply' a MoreArgs argument on the other side of the ellipsis:
Usage:
mapply(FUN, ..., MoreArgs = NULL, SIMPLIFY = TRUE,
USE.NAMES = TRUE)
So what happens if you try this:
mapply(assign, kkk$vars, kkk$vals, MoreArgs = list(envir = .GlobalEnv)
David Winsemius Alameda, CA, USA