matrix - How to average every 3 columns with NA in R -

i have matrix na , want find mean of every 3 columns each row.

set.seed(100) <- matrix(sample(c(na, 1:4), 90, replace = true), 10) 

if use

t(apply(a, 1, tapply, gl(3, 3), mean)) 

the code cannot find average colums including na. wonder how can modify code. lot.

we can converting 3d array , rowmeans after looping through 3rd margin.

res <- apply(array(a, c(nrow(a), 3, 3)), 3, rowmeans, na.rm = true) all.equal(res, t(apply(a, 1, tapply, gl(3, 3),         mean, na.rm = true)), check.attributes = false) #[1] true