[S] selecting different rows from sections of an array

[Jean_Adams@usgs.gov (Jean Adams)]

     I'm have difficulty figuring out how to select specific rows from 
     arrays inside a list.  The catch is that I want to select *different* 
     rows from different segments of the array.  Here's an example.  I've 
     got a list called stuff that contains two 3-dimensional arrays (the 
     reason stuff is a list instead of an array is due to earlier steps in 
     the program, where the sizes of the arrays are not the same).
     
     stuff <- list(array(1:24, dim=c(3, 4, 2)), 
        array(25:48, dim=c(3, 4, 2)))
     
     [[1]]:
     
     , , 1
          [,1] [,2] [,3] [,4] 
     [1,]    1    4    7   10
     [2,]    2    5    8   11
     [3,]    3    6    9   12
     
     , , 2
          [,1] [,2] [,3] [,4] 
     [1,]   13   16   19   22
     [2,]   14   17   20   23
     [3,]   15   18   21   24
     
     [[2]]:
     
     , , 1
          [,1] [,2] [,3] [,4] 
     [1,]   25   28   31   34
     [2,]   26   29   32   35
     [3,]   27   30   33   36
     
     , , 2
          [,1] [,2] [,3] [,4] 
     [1,]   37   40   43   46
     [2,]   38   41   44   47
     [3,]   39   42   45   48
     
     And I've got another 3-dimensional array, pickrow, which I would like 
     to use to select rows from the list above.  The data in the array are 
     the row numbers I would like to select, and so relate to dimension 1 
     in the arrays in stuff.  (Dimension 1 in pickrow relates to dimension 
     3 in stuff, and dimension 3 in pickrow relates to the list elements in 
     stuff.  Have I lost you yet?)
     
     pickrow <- array(sample(1:3, 12, T), dim=c(2, 3, 2))
     
     , , 1
          [,1] [,2] [,3] 
     [1,]    3    1    3
     [2,]    1    1    2
     
     , , 2
          [,1] [,2] [,3] 
     [1,]    1    1    2
     [2,]    3    3    3
     
     If I knew the magic words, I would be able to create a new list, 
     newstuff, that looked like this (dimnames unimportant):
     
     [[1]]:
     
     , , 1
          [,1] [,2] [,3] [,4] 
     [3,]    3    6    9   12
     [1,]    1    4    7   10
     [3,]    3    6    9   12
     
     , , 2
          [,1] [,2] [,3] [,4] 
     [1,]   13   16   19   22
     [1,]   13   16   19   22
     [2,]   14   17   20   23
     
     [[2]]:
     
     , , 1
          [,1] [,2] [,3] [,4] 
     [1,]   25   28   31   34
     [1,]   25   28   31   34
     [2,]   26   29   32   35
     
     , , 2
          [,1] [,2] [,3] [,4] 
     [3,]   39   42   45   48
     [3,]   39   42   45   48
     [3,]   39   42   45   48
     
     I would appreciate any suggestions you might be able to offer.  Send 
     them to me and I will summarize to the list.  Thanks.
     
     JVA
     
     
     Jean V. Adams                      USGS Biological Resources Division 
     e-mail: jean_adams@usgs.gov        Great Lakes Science Center
     phone:  (734) 214-9307             1451 Green Road
     FAX:    734-994-8780               Ann Arbor, MI 48105-2899  USA
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