[R] creating expressions inside loop

Jan Goebel jgoebel at diw.de
Fri Apr 27 16:35:41 CEST 2001


Hello all,

may be someone can give me a hint how to
solve a little problem.

I'm trying to create some expressions inside
a for-loop which i want to evaluate AFTER this
creation loop (but loop specific).

To explain my problem here comes the code:

y.mat <- t(matrix(rep(84:90,8) + as.numeric(gl(8,7)),nrow=7))

# > y.mat[1:2,]
#      [,1] [,2] [,3] [,4] [,5] [,6] [,7]
# [1,]   85   86   87   88   89   90   91
# [2,]   86   87   88   89   90   91   92

shift <- list()
for (i in 1:8) {
  shift[[i]] <- expression(
      eval(
           parse(text=paste("cbind(",
                   paste("w1", y.mat[i,],sep="",collapse = ", "),")")
                 )
           )
      )
}
# which gives no error, but

> dimnames(eval(shift[[1]]))[2]
[[1]]
[1] "w189" "w190" "w191" "w192" "w193" "w194" "w195"
> dimnames(eval(shift[[4]]))[2]
[[1]]
[1] "w189" "w190" "w191" "w192" "w193" "w194" "w195"

is all the same, because "i" is fixed by the last value
in the loop. So how can i change

> shift[1]
[[1]]
expression(eval(parse(text = paste("cbind(", paste("w1", y.mat[i,], 
    sep = "", collapse = ", "), ")"))))

to an "in-loop evaluating" of
> paste("w1", y.mat[i,],sep="",collapse = ", ")
[1] "w189, w190, w191, w192, w193, w194, w195"
  
so that the expression looks like
> shift[1]
[[1]]
expression(eval(parse(text = paste("cbind(", 
    "w189, w190, w191, w192, w193, w194, w195", ")"))))


hope this is understandable ;-)

best

jan
-- 
+-----------------------------------
 Jan Goebel (mailto:jgoebel at diw.de)

 DIW Berlin 
 Longitudinal Data and Microanalysis
 Königin-Luise-Str. 5
 D-14195 Berlin -- Germany --
 phone: 49 30 89789-377
+-----------------------------------
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