Upper.tri with an array in R

Question

I have a function that returns 300 arrays as follows:

 , , 38 [,1] [,2] [,3] [,4] [,5] [1,] 1.0000000 1.000000 1.000000 1.000000 1 [2,] 1.4457207 1.000000 1.000000 1.000000 1 [3,] 1.1491685 1.152171 1.000000 1.000000 1 [4,] 0.9009709 0.600254 1.444501 1.000000 1 [5,] 1.0620356 1.769513 1.147224 2.505219 1 , , 39 [,1] [,2] [,3] [,4] [,5] [1,] 1.0000000 1.0000000 1.0000000 1.000000 1 [2,] 1.0693369 1.0000000 1.0000000 1.000000 1 [3,] 1.8235562 1.6199451 1.0000000 1.000000 1 [4,] 0.6631731 0.9665938 0.2569683 1.000000 1 [5,] 0.7608913 2.3203717 0.7305705 4.549893 1 , , 40 [,1] [,2] [,3] [,4] [,5] [1,] 1.000000 1.0000000 1.000000 1.000000 1 [2,] 1.003870 1.0000000 1.000000 1.000000 1 [3,] 1.206578 0.8969491 1.000000 1.000000 1 [4,] 1.205347 1.2673170 1.345472 1.000000 1 [5,] 2.741506 2.0376783 1.151699 2.787262 1 

I would like to convert all the top ones (including the diagonal) to 0 .

 lapply(x,function(x) x[,,][upper.tri(x[,,],diag = T)] <- 0) 

but does not work. Any help please?

Answer 1

We can just use a for loop

 for(i in seq(dim(x)[3])) x[,,i][upper.tri(x[,,i], diag = TRUE)] <- 0 

gives

 x #, , 1 # [,1] [,2] [,3] [,4] [,5] #[1,] 0.0000000 0.000000000 0.0000000 0.0000000 0 #[2,] 0.5365853 0.000000000 0.0000000 0.0000000 0 #[3,] 0.4196231 -0.466495124 0.0000000 0.0000000 0 #[4,] -0.5836272 -0.848370044 -1.4290903 0.0000000 0 #[5,] 0.8474600 0.002311942 0.3322444 0.5163357 0 #, , 2 # [,1] [,2] [,3] [,4] [,5] #[1,] 0.00000000 0.0000000 0.0000000 0.0000000 0 #[2,] -0.08554095 0.0000000 0.0000000 0.0000000 0 #[3,] 0.11953107 0.6128514 0.0000000 0.0000000 0 #[4,] -0.11629639 1.5171225 0.1692267 0.0000000 0 #[5,] -0.94382724 0.6573804 -1.8221903 -0.2557446 0 #, , 3 # [,1] [,2] [,3] [,4] [,5] #[1,] 0.0000000 0.0000000 0.0000000 0.000000 0 #[2,] -1.0736261 0.0000000 0.0000000 0.000000 0 #[3,] 0.7696819 1.1782477 0.0000000 0.000000 0 #[4,] 1.7709054 1.0494212 1.3185662 0.000000 0 #[5,] -0.1961822 0.5609812 0.5713866 -1.567617 0 

data

 set.seed(24) x <- array(rnorm(5*5*3), dim = c(5, 5, 3))