以“ R”方式将函数应用于两个向量？

Question

There are two vectors x and y. If x contains an NA I want the NA to be replaced by a value from "y" with the corresponding index. Here is some example code that works:

x <- c(1,2,3,NA,5)
y <- c(6,7,8,9,10)

combineVector <- function(x,y)
{
  for (i in 1:length(x)){
  if (is.na(x[i]) && !is.na(y[i])){
      x[i] = y[i]
    }
  }  
   return (x) 
  }
combineVector(x,y)
# [1] 1 2 3 9 5

I could have written this in almost any programming language. Is there a more "R" way to perform this task?

Answer 1

x <- c(1,2,3,NA,5)
y <- c(6,7,8,9,10)

x[is.na(x)] <- y[is.na(x)]

See the above. using is.na() on x returns a logical vector where it is TRUE for the NA elements of x. Using these in the selector for X and Y will select only those NA elements. Using it in assignment will replace the NA elements from x with the corresponding ones from Y.

That will be much faster than looping as the vector gets large.

Answer 2

Try this code:

x[is.na(x)] <- y[is.na(x)]

By subsetting the x vector with is.na(x) you will be assigning only those values of x which are NA to the corresponding indices in the y vector.

Answer 3

To generate a new vector taking x and y as input, you can use the ifelse function:

x<-c(1,2,3,NA,NA)
y<-c(6,7,8,9,NA)
ifelse(is.na(x), y, x)
# [1]  1  2  3  9 NA