r - R中的累积乘法加上额外的常数

Question

我是 R 的新手，正在努力解决以下累积乘法与额外常量相加的组合。我希望在数据框中实现以下目标:

Variable_X         Variable_Y           Variable_Z
X1                 Y1                   Y1*X1      = Z1 
X2                 Y2                   (Z1+Y2)*X2 = Z2 
X3                 Y3                   (Z2+Y3)*X3 = Z3
X4                 Y4                   (Z3+Y4)*X4 = Z4

如有任何帮助，我们将不胜感激。

Answer 1

library(Rcpp)

cppFunction("NumericVector foo_cpp (NumericVector x, NumericVector y) {
  int n = x.size(), i;
  NumericVector z(n);
  double tmp = 0.0;
  for (i = 0; i < n; i++) {
    tmp = (tmp + y[i]) * x[i];
    z[i] = tmp;
    }
  return z;
  }")

set.seed(0)
dat <- data.frame(x = runif(1e+6), y = runif(1e+6))
system.time(z <- foo_cpp(dat$x, dat$y))
#   user  system elapsed 
#  0.016   0.000   0.014 
dat$z <- z