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extracting submatrix from a bigger one

William Dunlap 
What was suggested gave you a list of data.frames, each named with the ID .
You can use the syntax list$name or list[["name"]] to refer to a data.frame.
  R> splitData <- split(allData, allData$ID)
  R> splitData$x1
    ID value1 value2
  1 x1     10     12
  2 x1     12     22
  3 x1     11      9
  R> splitData$x2
    ID value1 value2
  4 x2     15     10

You seem to want a function that creates a bunch of data.frames in the
current environment instead of one that creates them in a list created to
hold them.  This is not necessary and actually gets in the way most of the
time.

If you want to refer to 'x1' instead of 'splitData$x1' you can use 'with', as in
  R> with(splitData, mean(x1$value2) - mean(x2$value2))
  [1] 4.333333
instead of the slightly wordier
  R> mean(splitData$x1$value2) - mean(splitData$x2$value2)
  [1] 4.333333

If you want to process each sub-data.frame (these are data.frame, not matrices)
you can use lapply() or sapply() or vapply() on the list
  R> dm <- sapply(splitData, function(x)mean(x$value2) - mean(x$value1))
  R> dm
         x1        x2        x3 
   3.333333 -5.000000 -2.500000
  R> dm["x2"]
  x2 
  -5

If you put all those names into the current environment you stand the chance
of clobbering some other dataset whose name matched one of the entries in
allData$ID.  Also you would have to use some rather ugly code involving get()
and assign() to manipulate the objects.  Learn to love lists.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

Thread (12 messages)

matteo dossena extracting submatrix from a bigger one Jun 24 Rui Barradas extracting submatrix from a bigger one Jun 24 matteo dossena extracting submatrix from a bigger one Jun 24 Bert Gunter extracting submatrix from a bigger one Jun 24 Rui Barradas extracting submatrix from a bigger one Jun 24 David Winsemius extracting submatrix from a bigger one Jun 24 David Winsemius extracting submatrix from a bigger one Jun 24 Rui Barradas extracting submatrix from a bigger one Jun 24 Bert Gunter extracting submatrix from a bigger one Jun 24 matteo dossena extracting submatrix from a bigger one Jun 24 Bert Gunter extracting submatrix from a bigger one Jun 24 William Dunlap extracting submatrix from a bigger one Jun 24