Question

I would like to extract elements from a deeply embedded list into an array.

For example, I am implementing a t-test at each grid point (2×2) and would like to save each p-value from the t-test into a 2×2 array without a nested for loop. (My data set is quite large.)

z <- rnorm(2*2*2)
z <- array(z, dim=c(2,2,2))

ttest <- apply(z, c(1,2), function(x) t.test(x, mu=.3, var.equal=TRUE))

ttest[[1,1]]$p.value    # extracts p-value at the first grid point.  
                        # This would be the [1,1] element in my desired array.

Answer 1

Do you want something like this:

> apply( ttest, 1:2, function(z) z[[1]]$p.value)
          [,1]       [,2]
[1,] 0.9030515 0.08736825
[2,] 0.7740801 0.35580602