move to left Rcpp version

library(data.table)
library(plyr)
library(dplyr)
library(magrittr)
library(Rcpp)

mat = fread('No, A, B, C, D, E, F, G
1, 1, 3, 0, 0, 4, 2, 1
2, 1, 0, 0, 0, 2, 0, 3
3, 0, 1, 0, 3, 0, 0, 0
4, 1, 3, 2, 1, 0, 0, 0
5, 0, 6, 0, 0, 0, 0, 0
6, 0, 0, 0, 0, 2, 2, 1
') %>% as.matrix

sourceCpp(code = '
#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
NumericMatrix move_left_f(NumericMatrix mat, double replacedValue = 0.0, bool drop = false) {
  int nc = mat.ncol(), nr = mat.nrow();
  std::vector< std::vector<double> > out(nr);
  for (int j =0; j < nc; j++)
  {
    for (int i = 0; i < nr; i++)
    {
      if (mat(i,j)!=replacedValue)
        out[i].push_back(mat(i,j));
    }
  }
  std::size_t outNumCol = 0;
  if (drop)
  {
    for (int i = 0; i < nr; i++)
      outNumCol = (outNumCol > out[i].size()) ? outNumCol : out[i].size();
  }
  else
    outNumCol = nc;
  NumericMatrix outMat(nr, outNumCol);
  for (int j = 0; j < (int) outNumCol; j++)
  {
    for (int i = 0; i < nr; i++)
    {
      if (j < (int) out[i].size())
        outMat(i, j) = out[i][j];
      else
        outMat(i, j) = 0.0;
    }
  }
  return outMat;
}')
move_left_f(mat, 0.0, FALSE)
#      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
# [1,]    1    1    3    4    2    1    0    0
# [2,]    2    1    2    3    0    0    0    0
# [3,]    3    1    3    0    0    0    0    0
# [4,]    4    1    3    2    1    0    0    0
# [5,]    5    6    0    0    0    0    0    0
# [6,]    6    2    2    1    0    0    0    0
move_left_f(mat, 0.0, TRUE)
#      [,1] [,2] [,3] [,4] [,5] [,6]
# [1,]    1    1    3    4    2    1
# [2,]    2    1    2    3    0    0
# [3,]    3    1    3    0    0    0
# [4,]    4    1    3    2    1    0
# [5,]    5    6    0    0    0    0
# [6,]    6    2    2    1    0    0