[R] problem creating an array

[Rui Barradas]

Hello,

You don't need the loop, it can be done with one much simpler instruction.
Since the number of rows is not important, the example uses a 10x603 matrix.

x <- matrix(seq_len(10*603), ncol = 603)
y <- array(x, dim = c(10, 3, 201))  # that's it

# See the first two
y[, , 1:2]

Hope this helps,

Rui Barradas
Em 13-09-2012 23:04, Curtis Burkhalter escreveu:
> Hello,
>
> I am having trouble creating a (1000,3,201) array in R from a data set
> created within the same script.  My problem is that I want to take a matrix
> that is 1000x603
> (called "landmat") and separate this into 201 separate (1000x3) matrices.
>   My problem is when I try to do particular combinations of the columns.  I
> want to take the first 3 columns of "landmat" and create the first 1000x3
> matrix, then I want to take columns 4,5,6 of "landmat" and create the
> second matrix, then continue this process until all 603 columns have been
> used resulting in the 201 unique 1000x3 matrices.  Any help would be
> appreciated and my code is pasted below:
>
> #========================================================================
> #landscape changes
> #========================================================================
> ##generate 3 sequences, each of length n=21; sequences named theta"n"_set1
> theta1_set1=c(seq(0,1,0.005))
> seqa=c(seq(0,0.50,0.005))
> seqb=c(seq(0.495,0,-0.005))
> theta2_set1=c(seqa,seqb)
> seqc=c(seq(1,0,-0.01))
> seqd=c(rep(0,100))
> theta3_set1=c(seqc,seqd)
> sum=numeric()
> for (i in 1:201)
> { sum[i]= theta1_set1[i]+theta2_set1[i]+theta3_set1[i]
> }
> sum
> #"n" designates the number of random #'s to be generated from rnorm
> #"x"combines all three strings of landscape scenarios into one vector
> #"sd" tells the std dev. used when generating #'s from rnorm
> #"p"indicates that x is 63 observation in length
> #mat" is a vector of randomly generated numbers from the normal dist'bn
> #using n, the first value of x and sd
> #designate a "for loop" that loops over the remaining observations in x
> #and inserts them as the mean of the normal distribution from which the
> #random numbers are generated
> n=1000
> x=c(theta1_set1,theta2_set1,theta3_set1)
> p = length(x)
>
> mat <- rep(x[1],n)
> for (i in 2:p) {
>
>          mat <- cbind(mat,rep(x[i],n))
> }
> #sort the matrix columns so that 201 unique landscape combinations are
> #created; each set of 3 columns should sum to one
> landmat=cbind(mat[,c(1)],mat[,c(202)],mat[,c(403)])
>
> for (i in 2:201)
> {
> landmat=cbind(landmat,(cbind(mat[,c(i)],mat[,c(i+201)],mat[,c(i+402)])))
> }
> ##this loop is a check to ensure the triplets all sum to 1
> #sum=numeric()
> #n=1
> #landmat_vec=landmat[1,]
> #for (i in 1:201)
> #{
> #sum[i]=landmat_vec[n]+landmat_vec[n+1]+landmat_vec[n+2]
> #n=n+3
> #}
>
>
> #create vector of column names in "hab" for each matrix and attach using
> #"colnames(matrix)"
> hab<-c("theta1","theta2","theta3")
> colnames(landmat)=rep(hab,201)
>
> *********The following for loop is not working******
> ## separate the columns of landmat(dim:1000x603)
> # into 201 separate 1000x3 matrices
>
> dims=c(1000,3,201)
> n=1
> landscape=array(dim=dims)
> for (i in 1:201)
> {
> landscape[i]=landmat[ ,c(n,n+1,n+2)]
> n=n+3
> }
>
>