[R] Odp: Sum of Product in a Matrix
Petr PIKAL
petr.pikal at precheza.cz
Wed Sep 23 09:24:28 CEST 2009
Hi
I am not sure if I understand what you want but if your matrix is not so
big you can try
> x[,1]*x[,2]
[1] 5 12 21 32
> cumsum(x[,1]*x[,2])
[1] 5 17 38 70
>
and than check value of cumsum according to your condition.
Regards
Petr
r-help-bounces at r-project.org napsal dne 23.09.2009 05:25:16:
>
> Hi,
> I am new in R and I don´t know how to sum the product of two elements at
the
> time in a matrix
>
> X=[ 1 5 9 13
> 2 6 10 14
> 3 7 11 15
> 4 8 12 16]
> I would like to do (1*5+2*6+3*7+4*8)
> I need to do it step by step because I will further put a conditional in
the
> formula
>
> It worked this way
> x <- matrix ( c (1 : 16),ncol = 4) #generating my x matrix
> qw <- matrix (0, ncol = 4, nrow = 4)
> answer<- matrix (0, ncol = 4, nrow = 4) #my final objective is to
generate
> this matrix
> soma <- function (d,q){
> (d [q, 1] * d [q, 2]) #a function to multiplicate two collumns and two
> elements at a time
> }
> for (q in 1:4){
> m <- soma
> qw [q, 2] <- m (d, q)
> }
> answer <- sum (qw [, 2])
>
> However I am doing this to generate a X'X matrix (since I can´t do
t(X)$*$X
> because i would like to include a conditional in the formula. Threrefore
> this script above is not good to me)
>
> Could anybody help me?
> Thanks in advance
> --
> View this message in context: http://www.nabble.com/Sum-of-Product-in-a-
> Matrix-tp25530977p25530977.html
> Sent from the R help mailing list archive at Nabble.com.
>
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