On Aug 29, 2010, at 8:47 PM, Lorenzo Cattarino wrote:
> Hi,
>
>
>
> I have the following matrix
>
>
>
> cc <- matrix (1:21, 3)
>
> cc[,3:4]<- 0
>
> cc
>
> [,1] [,2] [,3] [,4] [,5] [,6] [,7]
>
> [1,] 1 4 0 0 13 16 19
>
> [2,] 2 5 0 0 14 17 20
>
> [3,] 3 6 0 0 15 18 21
>
>
>
> and I would like to sum just the values in columns 2, 3 and 4, so to
> have something like
>
>
>
> 1 4 13 16 19
>
> 2 5 14 17 20
>
> 3 6 15 18 21
To take only selected columns:
> CC <-cc[,c(1,2,5,6,7)]
> CC
[,1] [,2] [,3] [,4] [,5]
[1,] 1 4 13 16 19
[2,] 2 5 14 17 20
[3,] 3 6 15 18 21
I'm having difficulty understanding the point of summing columns which
you have just set to zero so am taking the liberty of changing the
task to summing columns 2-4 and leaving in column 2 of the shortened
matrix:
> CC[,2] <-apply(cc[ , 2:4], 1, sum)
> CC
[,1] [,2] [,3] [,4] [,5]
[1,] 1 21 13 16 19
[2,] 2 24 14 17 20
[3,] 3 27 15 18 21>
>
>
> Thanks
>
>
>
> Lorenzo
>
>
> [[alternative HTML version deleted]]
>
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