R help - Apr 2001 - creating expressions inside loop

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
 K?nigin-Luise-Str. 5
 D-14195 Berlin -- Germany --
 phone: 49 30 89789-377
+-----------------------------------
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Jan Goebel <jgoebel at diw.de> writes:
> 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
You could use

  substitute(...., list(i=i))

instead of 

  expression(....)

But wouldn't you rather do something like

f <- function(row) {
    n <- paste("w1",row, sep="")
    m <- do.call("cbind", lapply(n, get))
    names(m) <- n
    m
}

apply(y.mat, 1, f)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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