Stack benchmarking

stack.r

new_stack = function(capacity){
    size = 0
    items = vector("numeric", capacity)

    add = function(x){
        size <<- size + 1
        items[size] <<- x
        }

    get = function(){
        items[seq_len(size)]
        }

    environment()
    }



new_stack2 = function(n){
    items = numeric()

    add = function(x){
        items <<- c(items, x)
        }

    get = function(){
        items
        }

    environment()
    }


test = function(stack, n = 1000, every = 1){
    for(i in seq_len(n)){
        stack$add(i)
        if(!i %% every)
            stack$get()
        }
    }


# for small n and small every, there is no value in pre-allocating
# for n~100 and every~4, there is very little difference
# for n~1000 and every~100, the pre-allocated stack is ~2x faster and 40x more memory efficient

n = 1000
every = 100
bench::mark(
    test(new_stack(n), n, every),
    test(new_stack2(), n, every)
    )