How can I create Variables A1,A2,...,A100 using a loop in R?

Question

I am trying to create 1000 variables, which I want to name with the index number. I don't know how to create these new variables.

for(i in 1:1000) {
  Ui <- rnorm(200,0,1)
}

Answer 1

This is a common sort of thing that people want to do, especially when they are coming from other programming languages. However, there are better ways to accomplish the same thing, and you should not follow recommendations to use assign; that is bad advice that you will likely regret later on.

The way we do this sort of thing in R is to use lists, specifically named lists:

x <- replicate(1000,rnorm(200,0,1),simplify = FALSE)
x <- setNames(x,paste0("A",seq_along(x)))

Now x is a named list of length 1000, each element is a vector of length 200 from a normal(0,1) distribution.

You can refer to each one via x[[1]] or x[["A1"]] as needed. Additionally, since they are all in the same object, you can operate on the easily as a group using tools like lapply.

Pretty much any time you find yourself wanting to create a sequence of objects with similar names, that should be a signal to you that you should be using a list instead.

Answer 2

There is no point in cluttering your environment with so many variables, try to store them in a named list instead

l1 <- setNames(lapply(1:5, function(x) rnorm(5)), paste0("A", 1:5))
l1

#$A1
#[1]  0.4951453 -1.4278665  0.5680115  0.3537730 -0.7757363

#$A2
#[1] -0.11096037  0.05958700  0.02578168  1.00591996  0.54852030

#$A3
#[1]  0.1058318  0.6988443 -0.8213525 -0.1072289  0.8757669

#$A4
#[1] -0.6629634  0.8321713 -0.3073465 -0.2645550 -1.0064132

#$A5
#[1]  2.2191246  0.2054360 -0.1768357  1.6875302 -1.1495807

Now you can access individual list element as

l1[["A1"]]
#[1] 0.4951453 -1.4278665  0.5680115  0.3537730 -0.7757363

---

Moreover, other method is to generate all the numbers together and then split them into list.

groups = 5
each = 5

setNames(split(rnorm(groups * each), rep(seq_len(groups), each = each)), 
         paste0("A", seq_len(groups)))

Answer 3

I agree with the others that this is not a good idea. Anyway, to answer your question how you wolud do that is

k <- 1000 # number of variables
n <- 200 # sample size of each variable
for(i in 1:k){
assign(paste0("variable", i), rnorm(n, 0, 1))}
variable1
-0.012947062  0.728284959 -1.627796366  0.003471491 ...

However, personally I would prefer another solution. The both answers so far suggest using lists. I find lsts quite cumbersome, especially if you are new to R. So I would suggest creating a matrix where every column contains one variable.

# creates a matrix
m <- matrix(rep(NA, n*k), ncol= k)
# generates rnorm() in each column
for(i in 1:k){
m[ , i] <- rnorm(n, 0, 1)
}

# now you can name the columns
colnames(m) <- paste0("variable", 1:k)
m
        variable1   variable2    ...
 [1,]  0.30950749 -2.07388046
 [2,] -1.13232330 -0.55511476
  ...