[R] how to resample (or resize) matrix?

[Robin Hankin]

Right, I think I understand the question.



library(magic)
?subsums

If you want a windowed moving average, do:

x <- matrix(1:100,10,10)
subsums(x,6,FUN="mean",pad=NA,wrap=F)[6:10,6:10]



If you want block average, do:

subsums(x,2,FUN="mean",pad=NA,wrap=F)[seq(2,10,2),seq(2,10,2)]

which agrees with Jim's solution below.


HTH

rksh




On 27 Jul 2006, at 11:20, jim holtman wrote:

> Is this what you want: the mean of the surrounding 4 cells?
>
>> x <- matrix(1:100, 10)  # create data
>> rmean <- matrix(0,5,5)  # result matrix
>> for (i in 1:5){
> +     for (j in 1:5){
> +         rmean[i, j] <- mean(x[c(-1,0) + 2 * i, c(-1,0) + 2 * j])
> +     }
> + }
>> x
>       [,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,]    3   13   23   33   43   53   63   73   83    93
>  [4,]    4   14   24   34   44   54   64   74   84    94
>  [5,]    5   15   25   35   45   55   65   75   85    95
>  [6,]    6   16   26   36   46   56   66   76   86    96
>  [7,]    7   17   27   37   47   57   67   77   87    97
>  [8,]    8   18   28   38   48   58   68   78   88    98
>  [9,]    9   19   29   39   49   59   69   79   89    99
> [10,]   10   20   30   40   50   60   70   80   90   100
>> rmean
>      [,1] [,2] [,3] [,4] [,5]
> [1,]  6.5 26.5 46.5 66.5 86.5
> [2,]  8.5 28.5 48.5 68.5 88.5
> [3,] 10.5 30.5 50.5 70.5 90.5
> [4,] 12.5 32.5 52.5 72.5 92.5
> [5,] 14.5 34.5 54.5 74.5 94.5
>>
>
>
>
> On 7/27/06, Vladimir Eremeev <wl at eimb.ru> wrote:
>>
>> Dear r-help,
>>
>> I have a matrix, suppose, 10x10, and I need the matrix 5x5, having
>> in each cell a mean value of the cells from the initial matrix.
>>
>> Please, point me to a function in R, which can help me doing that.
>>
>> Digging the documentation and mail archives didn't give me a result.
>>
>> Thank you.
>>
>> ---
>> Best regards,
>> Vladimir                mailto:wl at eimb.ru
>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
>
> --  
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390
>
> What is the problem you are trying to solve?
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting- 
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743