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Data frames

2 messages · Josef Eschgfaeller, Eric Lecoutre

Josef Eschgfaeller
# 
I have two questions about data frames:

(1) How can one extract a simple matrix
from a data frame? I tried

      Matrixfromdf = function (frame,without=1)
      {a=frame[colnames(frame)[-without]]
      v=unlist(a,use.names=F)
      matrix(v,ncol=ncol(a))}

but it works well only for without=1,
perhaps also because the function in (2)
gives probably a different meaning to
the first column.

(2) How does one define a void data frame
with only column names but no values?
I tried this indirect way:

     # Void df with titles from ...
     Newvoid = function (...)
     {a=c(...); m=length(a)
     titles=paste(a,collapse=' ')
     conn=textConnection(titles)
     tab=read.table(conn,header=T)
     close(conn); tab}

Thanks
Josef Eschgf??ller
Eric Lecoutre
# 
?as.matrix
data(iris)
as.matrix(iris[,-5]) # numeric
as.matrix(iris[,-1]) # character
Basically, you have to create the sctruture by providing one observation
This will allow you to specify the classes of the variables.
[1] x y
<0 rows> (or 0-length row.names)


Eric