How to fill in the preceding numbers whenever there is a 0 in R?

Question

I have a string of numbers:

n1 = c(1, 1, 0, 6, 0, 0, 10, 10, 11, 12, 0, 0, 19, 23, 0, 0)

I need to replace 0 with the corresponding number righ

Answer 1

Don't forget the simplicity and performance gain of Rcpp...

Using Arun's sample size I get...

Unit: milliseconds
                                  expr       min        lq    median        uq      max neval
                         rollValue(n1)  3.998953  4.105954  5.803294  8.774286 36.52492   100
 n1[cummax(seq_along(n1) * (n1 != 0))] 17.634569 18.295344 20.698524 23.104847 74.72795   100

The .cpp file to source is simply...

#include 
using namespace Rcpp;

// [[Rcpp::plugins("cpp11")]]

// [[Rcpp::export]]
NumericVector rollValue(const NumericVector v) {
  auto out = clone(v);
  auto tmp = v[0];
  for( auto & e : out) {
    if( e == 0 ) {
      e = tmp;
      continue;
    }
    tmp = e;
  }
  return out;
}