For the life of me I couldn't work out what to searc
I have an m*n numeric matrix x and a numeric vector y (of length m+n-1)
How do I do a calculation like this?
z[i,j] = x[i,j] * y[i+j] ?
Well, one can write a pair of loops, or write a single loop
within which we calculate a vector at a time, but ...
is there a "neat" way to do it?
tiny example:
x<-matrix(data=c(32,46,21,28,58,60,33,32,16,NA,10,15),nrow=4)
y<-c(1.1,1.09,1.08,1.06,1.05,1.02)
z<-matrix(nrow=4,ncol=3)
z[,1]=x[,1]*y[1:4]
z[,2]=x[,2]*y[2:5]
z[,3]=x[,3]*y[3:6]
which produces:
> x
[,1] [,2] [,3]
[1,] 32 58 16
[2,] 46 60 NA
[3,] 21 33 10
[4,] 28 32 15
> y
[1] 1.10 1.09 1.08 1.06 1.05 1.02
> z
[,1] [,2] [,3]
[1,] 35.20 63.22 17.28
[2,] 50.14 64.80 NA
[3,] 22.68 34.98 10.50
[4,] 29.68 33.60 15.30
> z/x
[,1] [,2] [,3]
[1,] 1.10 1.09 1.08
[2,] 1.09 1.08 NA
[3,] 1.08 1.06 1.05
[4,] 1.06 1.05 1.02
(this last to indicate what each element of x was multiplied by to produce
z... well, apart from the NA)
Thanks for any pointers
Glen
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