这在写答案时可能不存在，但由于我带着同样的问题来到这里并找到了更好的解决方案，这里是为未来的 googlers 准备的:

This probably didn't exist when the answers were written, but since I came here with the same question and found a better solution, here it is for future googlers:

你想要的是 dplyr 中的 coalesce() 函数:

What you want is the coalesce() function from dplyr:

y <- c(1, 2, NA, NA, 5)
z <- c(NA, NA, 3, 4, 5)
coalesce(y, z)

[1] 1 2 3 4 5