Summary: simple array arithmetic

["Jean V Adams" <jvadams@usgs.gov>]

Thanks to Brad Biggerstaff, Pravin Jadhav, and Patrick Burns for their
quick and helpful responses.  All three of the following one-line commands
did the trick (original posting follows):
      a + 10 * array(b, dim=c(3, 4, 2))
      a + 10 * as.vector(b)
      sweep(a, 1:2, 10*b, "+")

JVA


                                                                                
                                                         
                      "Jean V Adams"                                            
                                                         
                      <jvadams@usgs.gov>               To:       
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                      s-news-owner@lists.biosta        Subject:  [S] simple 
array arithmetic                                             
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                      05/14/2004 02:46 PM                                       
                                                         
                                                                                
                                                         
                                                                                
                                                         


I can't seem to figure out how to do a simple arithmetic operation with an
array and a matrix.  I want to add a matrix to each "matrix part" of an
array, and get a result with the same structure as the array.

Here's an example:

a <- array(1:24, dim=c(3, 4, 2))
b <- matrix(1:12, nrow=3)

a
, , 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

b
     [,1] [,2] [,3] [,4]
[1,]    1    4    7   10
[2,]    2    5    8   11
[3,]    3    6    9   12

> >
What I want to end up with is
, , 1
     [,1] [,2] [,3] [,4]
[1,]   11   44   77  110
[2,]   22   55   88  121
[3,]   33   66   99  132
, , 2
     [,1] [,2] [,3] [,4]
[1,]   23   56   19  122
[2,]   34   67  100  133
[3,]   45   78  111  144

But, when I try what seems to me to be the obvious approach,
      apply(a, 3, "+", 10*b)
I get this:

      [,1] [,2]
 [1,]   11   23
 [2,]   22   34
 [3,]   33   45
 [4,]   44   56
 [5,]   55   67
 [6,]   66   78
 [7,]   77   89
 [8,]   88  100
 [9,]   99  111
[10,]  110  122
[11,]  121  133
[12,]  132  144

I can't figure out why the matrix structure (the dimensionality) wasn't
kept.  I'd appreciate someone setting me straight.

JVA

`·.,,  ><(((º>   `·.,,  ><(((º>   `·.,,  ><(((º>

Jean V. Adams
Statistician
U.S. Geological Survey
Great Lakes Science Center
c/o Marquette Biological Station
1924 Industrial Parkway
Marquette, MI 49855  U.S.A.
phone: (906) 226-1212
FAX: 906-226-3632
web site: www.glsc.usgs.gov
e-mail: JVAdams@usgs.gov