Suppose there is loop

x <- c(2,5,3,9,8,11,6)
count <- 0
for (val in x) {
if(val %% 2 == 0)  count = count 1
}

and there is flag variable. How to do that if flag=TRUE then run this loop and if flag has any other value then ignore run loop.Just continue to execute the rest of the code.

CodePudding user response：

Several alternatives:

1. Don't loop if !flag:

   flag <- FALSE
   x <- c(2,5,3,9,8,11,6)
   count <- 0
   if (flag) {
     for (val in x) {
       if(val %% 2 == 0)  count = count 1
     }
   }
   count
   # [1] 0
   

2. break out of the loop early:

   flag <- FALSE
   x <- c(2,5,3,9,8,11,6)
   count <- 0
   for (val in x) {
     if (!flag) break
     if(val %% 2 == 0)  count = count 1
   }
   count
   # [1] 0
   

3. while loop, self-incrementing the loop, and break out if !flag. I'm not going to code this, since it adds no benefit to #1 yet adds the risk that unconstrained (if poorly-written) while loops can introduce.

4. Avoid the loop, do this directly:

   flag <- FLASE
   sum(flag & x %% 2 == 0)
   # [1] 0
   
   flag <- TRUE
   sum(flag & x %% 2 == 0)
   # [1] 3