r - efficient vectorizisation of a double for loop -

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how can 1 vectorize following double loop in r?

a <-  seq(1,10, length=5) b <- seq(0,1, length=4) fun <- function(a,b){return(a+b)}  out <- matrix(nan, nrow=5, ncol=4)    for(i in 1:5) {     for(j in 1:4) {       out[i, j] <- fun(a[i], b[j])     }   }

i have attempted, example, without success. please advise, in advance

outer(1:nrow(out), 1:ncol(out), fun = fun(a,b)) mapply(out, fun)

what about:

outer(a, b, '+')  ## > outer(a, b, '+') ##       [,1]      [,2]      [,3]  [,4] ## [1,]  1.00  1.333333  1.666667  2.00 ## [2,]  3.25  3.583333  3.916667  4.25 ## [3,]  5.50  5.833333  6.166667  6.50 ## [4,]  7.75  8.083333  8.416667  8.75 ## [5,] 10.00 10.333333 10.666667 11.00

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