在for循环中在R中创建列

Question

I have a data frame in R and I would like to create new columns within a for loop. I have tried many things for the last 2 days but without success. At the end, I did find a solution that seems to work, but it doesn't seem very straight forward. I was wondering if anybody has a more elegant way to do this.
Sorry if this has already been addressed but I couldn't find similar question on SO
Here is my example.

x <- runif(20)
a <- as.data.frame(x)
for (i in 1:100){
  d <- x + i
  a <- cbind(a, d)
}

c <- 1
for (i in 1:100){
  c[i] <- paste0("colum", i)
    }
colnames(a) <- c("x", c)

Thanks in advance for any good suggestions to make this process all within one loop instead of 2.

Answer 1

Why not:

a[2:11] <- sapply(1:10, "+", a[[1]])

The names would be:

names(a) <- c("x", paste0("column", 1:10))

Answer 2

In this case you can avoid both loops. In R you should always try to use vectorised statements when possible. In this case you can do this using addition fairly easily, one way is

result <- matrix(x + rep(0:100, length(x)), ncol = 101, byrow = TRUE)
result <- as.data.frame(result)
names(result) <- c("x", paste0("column", 1:100))

You can also keep the matrix structure if you only want to store numbers. Also, you should avoid using cbind , rbind and other functions that increase the size of an object with each iteration in loops. The R inferno is a good book to read.

Answer 3

Perhaps what you are looking for is eval and parse , as such:

for (i in 1:100) {
    eval(parse(text = paste0('a$colum', i, ' <- whatever_you_want_your_column_to_contain'))
}

This will create named columns and their contents in a single statement.