R Break and Next

Break and next are two control statements that change how a loop behaves from inside. Break stops the loop entirely. Next skips the rest of the current iteration and jumps to the next one. Both give you fine-grained control over loop execution.

The break Statement

Diagram:
  Loop running...
      │
      ├── Iteration 1 ✓
      ├── Iteration 2 ✓
      ├── Iteration 3 → break! ──► EXIT LOOP
      ├── Iteration 4 (never reached)
      └── Iteration 5 (never reached)

for (i in 1:10) {
  if (i == 4) break
  cat(i, "")
}

Output:

1 2 3

The loop stops the moment i equals 4. Values 4 through 10 are never processed.

Practical break Example: Search in a List

products <- c("pen", "book", "ruler", "eraser", "sharpener")
target   <- "ruler"
found    <- FALSE

for (i in seq_along(products)) {
  if (products[i] == target) {
    cat("Found '", target, "' at position", i, "\n")
    found <- TRUE
    break   # no need to keep searching
  }
}

if (!found) cat("Product not found\n")

Output:

Found ' ruler ' at position 3

The next Statement

Diagram:
  Loop running...
      │
      ├── Iteration 1 ✓ (fully runs)
      ├── Iteration 2 → next! → skip rest → go to Iteration 3
      ├── Iteration 3 ✓ (fully runs)
      └── Iteration 4 ✓ (fully runs)

for (i in 1:6) {
  if (i %% 2 == 0) next   # skip even numbers
  cat(i, "")
}

Output:

1 3 5

When i is even (2, 4, 6), next jumps to the next iteration. The cat() line never runs for even numbers.

Practical next Example: Skip Missing Values

readings <- c(23, NA, 45, NA, 12, 38, NA, 51)
total    <- 0
count    <- 0

for (r in readings) {
  if (is.na(r)) next    # skip missing readings
  total <- total + r
  count <- count + 1
}

cat("Valid readings:", count, "\n")
cat("Average:", total / count, "\n")

Output:

Valid readings: 5
Average: 33.8

Using break and next Together

for (i in 1:20) {
  if (i %% 2 == 0) next    # skip even numbers
  if (i > 10) break        # stop after 10
  cat(i, "")
}

Output:

1 3 5 7 9

break Inside Nested Loops

Break only exits the innermost loop it is placed in:

for (i in 1:3) {
  for (j in 1:3) {
    if (j == 2) break    # exits only the inner loop
    cat(i, j, " | ")
  }
}

Output:

1 1  |  2 1  |  3 1  |

Quick Comparison

Statement   Effect on Loop
──────────────────────────────────────────────────────
break       Stops the loop immediately, exits completely
next        Skips the current iteration, continues to next

Break is ideal for search operations — stop when you find what you need. Next is ideal for filtering — process only items that meet a condition. Together they make loops much more efficient by avoiding unnecessary processing.