C vs base R

which_min.r

.which_min = inline::cfunction(
    sig = signature("vec" = "SEXP"),
    body = '
        int* v = INTEGER(vec);
        int min = v[0];
        size_t index = 1;
        size_t n = (size_t) XLENGTH(vec);
        for(int i = 0; i < n; i++){
            if(v[i] < min){
                min = v[i];
                index = i + 1;
                }
            }

        SEXP r = PROTECT(Rf_allocVector(INTSXP, 2));

        INTEGER(r)[0] = min;
        INTEGER(r)[1] = index;

        UNPROTECT(1);

        return r;
        ',
    language = "C",
        convention = ".Call"
    )

which_min_c = function(x){
    x = as.integer(x)
    y = .which_min(x)
    names(y) = c("min", "index")
    y
    }

which_min_b = function(x){
    i = which.min(x)
    m = x[i]
    c("min" = m, "index" = i)
    }


s = sample.int(n = 100000, size = 1e8, replace = TRUE)
s1 = s; s1[1] = 0L
s2 = s; s2[length(s) %/% 2] = 0L
s3 = s; s3[length(s)] = 0L

microbenchmark::microbenchmark(
    which.min(s1), which_min_c(s1), which_min_b(s1)
    )

microbenchmark::microbenchmark(
    which.min(s2), which_min_c(s2), which_min_b(s2)
    )

microbenchmark::microbenchmark(
    which.min(s3), which_min_c(s3), which_min_b(s3)
    )