leastOccurrences method

@useResult Occurrence<int>? leastOccurrences()

Returns an Occurrence of the least common value and its frequency, or null if the iterable is empty. Audited: 2026-06-12 11:26 EDT

Implementation

@useResult
Occurrence<int>? leastOccurrences() {
  // check if the list is empty before calling reduce
  if (isEmpty) {
    return null;
  }

  // Create a new HashMap to store each integer and its frequency.
  final HashMap<int, int> frequencyMap = HashMap<int, int>();
  // Iterate over each integer in the list.
  for (final int item in this) {
    // Update the frequency of the current integer in the map, or
    // set it to 1 if it's not in the map yet.
    // ignore: saropa_lints/require_future_error_handling -- Map.update is synchronous; there is no future to handle
    frequencyMap.update(item, (int value) => value + 1, ifAbsent: () => 1);
  }

  // Find the key-value pair with the lowest value (frequency) in the map.
  // The map is guaranteed non-empty since we checked isEmpty above.
  MapEntry<int, int>? leastCommonEntry;
  for (final MapEntry<int, int> entry in frequencyMap.entries) {
    if (leastCommonEntry == null || entry.value < leastCommonEntry.value) {
      leastCommonEntry = entry;
    }
  }

  if (leastCommonEntry == null) {
    return null;
  }

  return Occurrence<int>(leastCommonEntry.key, leastCommonEntry.value);
}