Increase counter in a for loop in R

counter, for-loop, r

Solution

`ifelse` is vectorized so no need to use a `for-loop` here. This how you should use it:

set.seed(10) 
x <- runif(20)
f <- ifelse(x<0.5, 'a', 'b')

Then Use `table` to count occurrence:

table(f)
f
 a  b 
13  7

To get `n1` :

n1 <- table(f)[['a']]

EDIT OP wants to change the sample according to the occurrence of a and b. You should use `if` and `else` not `ifelse`. You should also preallocate memory for vector f.

n1 <- 0 ; n2 <- 0
N <- 20
f <- vector(mode='character',N)
set.seed(10)
x<- runif(N)
for(i in seq(N)) {
     if (x[i] <0.5){ 
        f[i] <- 'a'
        n1 <- n1 +1
     } else {
        f[i] <- 'b'
        n2 <- n2 +1
     }
    if((n1-n2)==2) x <- runif(N)  ## condition to regenerate sample
}

Problem

Hello everyone i have a problem with a counter i have created in a for loop. Here is the code. ``` n1<- 0 n2<- 0 n<- 20 f<- rep(NA,20) set.seed(10) x<- runif(20) for(i in 1:20) { f[i]<- ifelse(x[i]<0.5, 'a', 'b') if((n1-n2)==2) { break } if(f[i]=='a') n1<- n1 + 1 else n2<- n2 + 1 # n1 counts a's n2 counts b's } [1] "b" "a" "a" "b" "a" "a" "a" NA NA NA NA NA NA NA NA NA NA NA NA NA ``` As you can see from the result number of a's=5 and b's=2 . But when i call n1 and n2 it returns 4 for n1 which is wrong . Why is that? How am I wrong ? Thanks in advance . I start sampling a's and b's with probability 0.5 .20 total. At some point which i dont know in advance, the number of a's - the number of b's exceeds 2. When this happens i want the sampling probability to change to 0.2 Thats what i am trying to achieve.

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