Question

I a having a little trouble with vector or array operations.

I have three 3D arrays and i wanna find the average of them. How can i do that? we can’t use mean() as it only returns a single value.

The more important is some of the cells in the arrays are NA whic mean if i just add them like

A = (B + C + D)/3 

The results of will show NA as well.

How can i let it recognise if the cell is NA then just skip it.

Like

 A = c(NA, 10, 15, 15, NA)
 B = c(10, 15, NA, 22, NA)
 C = c(NA, NA, 20, 26, NA)

I wanna the output of average these vectors be

(10, (10+15)/2, (15+20)/2, (15+22+26)/3, NA)

We also can’t use na.omit, because it will move the order of indexes.

This is the corresponding code. i wish it would be helpful.

for (yr in 1950:2011) {
    temp_JFM <- sst5_sst2[,,year5_sst2==yr & (month5_sst2>=1 & month5_sst2<=3)]
       k = 0
       jfm=4*k+1
    for (i in 1:72) {
        for (j in 1:36) {
            iposst5_sst2[i,j,jfm] <- (temp_JFM[i,j,1]+temp_JFM[i,j,2]+temp_JFM[i,j,3])/3
        }
    }      
}

Thnk you.

It already been solved.

The easiest way to correct it can be shown below.

iposst5_sst2[i,j,jfm] <- mean(temp_JFM[i,j,],na.rm=TRUE)

Answer 1

Here’s an example which makes a vector of the three values, which makes na.omit usable:

vectorAverage <- function(A,B,C) {
    Z <- rep(NA, length(A))

    for (i in 1:length(A)) {
        x <- na.omit(c(A[i],B[i],C[i]))
        if (length(x) > 0) Z[i] = mean(x)
    }
    Z
}

Resulting in:

vectorAverage(A,B,C)
[1] 10.0 12.5 17.5 21.0   NA

Edited: Missed the NaN in the output of the first version.