Question

I have two matrices I want to perform a loop on. My problem is I am looping for one colomn and do not know how to include the other column, hence my incorrect results. My codes are as below:

t=as.matrix(b)
y=as.matrix(a)
t
            a     b 
      [1,]  1     10
      [2,] NA      9
      [3,]  3     NA
      [4,]  4      7
      [5,]  5      6
      [6,]  3      4

y
              c      d
      [1,]    3     12
      [2,]    NA     11
      [3,]    5     NA
      [4,]    6      9
      [5,]    7      8
      [6,]    3     12

turn
     [,1]    [,2]
[1,]    0      0
[2,]    0      0

Code:

n=3  #number to consider at a time
runs=2 #total data points divided by 60 to the nearest whole number
turn=matrix(0, nrow=runs,2)
TR = y/t

for (i in 1: runs){
  index_start=3*(i-1)+1
  index_end= 3*i
  turn[i]=mean( TR[index_start:index_end],na.rm=TRUE)
}



turn
     [,1]      [,2]
[1,] 2.333333    0
[2,] 1.300000    0

The turn output has given correct results for the first column but, as expected, incorrect results for the second column. How do I adjust my loop function? Thank you in advance.

Answer 1

Look at the line

turn[i]=mean( TR[index_start:index_end],na.rm=TRUE)

If you only give a single number in the index of a matrix, it will work out the position by counting down the first column, then down the second, and so on.

So turn[1] refers to the element in the top left corner of the matrix turn, and turn[2] refers to the bottom left corner.

In your loop, i takes the values 1:runs, and runs is 2, so you only assign things to the first two elements of turn.