[R] Matrix manipulation

[David Winsemius]

On Jun 11, 2009, at 2:53 PM, Payam Minoofar wrote:

> Hello everyone,
>
> I have a couple of fairly simple questions (I hope) the answers to  
> which I cannot find through the documentation at the moment.
>
>
> 1.  I would like to delete the a row from a matrix if a certain  
> elimination criterion is met. I am familiar with x <- x[-7,] (to  
> remove row 7, for example). Are there any other means of removing an  
> entire row?

?which   # useful for converting logical vectors into argument for  
functions that require numerics

M10 <- matrix(1:100, nrow = 10)

# find row with 63
which( sapply( 1:10, function(x) 63 %in% M10[x, ]) )
[1] 3

M10[-which( sapply( 1:10, function(x) 63 %in% M10[x, ]) ), ]   #  
remove row with 63

       [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
  [1,]    1   11   21   31   41   51   61   71   81    91
  [2,]    2   12   22   32   42   52   62   72   82    92
  [3,]    4   14   24   34   44   54   64   74   84    94
  [4,]    5   15   25   35   45   55   65   75   85    95
  [5,]    6   16   26   36   46   56   66   76   86    96
  [6,]    7   17   27   37   47   57   67   77   87    97
  [7,]    8   18   28   38   48   58   68   78   88    98
  [8,]    9   19   29   39   49   59   69   79   89    99
  [9,]   10   20   30   40   50   60   70   80   90   100

>  2.  Is there a single command that will rename the index of each  
> row to match the row number once a row has been deleted. For  
> example, when row 7 is deleted above, the old row 8 is now row 7,  
> but the row name is still "8". I have figured out how to assign a  
> sequence vector to the row names, but I am wondering if there is a  
> built-in command that does the same thing. (I.e., change the name of  
> row 7 to "7" from "8".)
>
> Thank you very much.
>
> Payam
> --
> Payam Minoofar, Ph.D.
> Scientist
> Meissner Filtration Products
> 4181 Calle Tesoro
> Camarillo, CA 93012
> USA
> +1 805 388 9911
> +1 805 388 5948 fax
> Payam.minoofar at meissner.com
>
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT