Use the previous value if condition is met in R while using ifelse()

I came across an issue while converting one of if.. else condition to ifelse () in R to make the process faster. In this question, I have to use the value from the previous row if the condition is met. I was not able to replicate the same results from my code Below is the if.. else statement and its converted code.

for (i in 1:nrow(newdata)){

if ((newdata$first == 1)){
  newdata[, decvar][i] = groups + 1 - ceiling(round((newdata$cum/total) * groups, 4))
} #calculate decile; if var = 0, decile = 0
else if (newdata$first == 0){
  newdata[, decvar][i] = newdata[, decvar][i-1]
}

}

Using ifelse():

brv_trx1$decvar <- ifelse(((brv_trx1$first == 1)),(11 - ceiling(round((brv_trx1$cum/total) * 10, 4))), ifelse(((brv_trx1$first == 0)), lag(brv_trx1$decvar) ,NA))

The sample output will look something like this :

variable First Decvar

45 1 10

42 1 10

31 1 9

30 0 9

30 0 9

29 0 8

29 0 8

28 0 8

21 1 7

I was getting some output as 0, which I have no clue where it came from