How to Sort List of Week Day names in flutter in ascending order

The issue you’re going to have to overcome is that there is no super easy way to get a listing of the days of the week. However, that isn’t actually a difficult issue to deal with if you’re only needing to deal with this for english – you can just hardcode it.

Here’s an example:

const weekDays = [
  "Monday",
  "Tuesday",
  "Wednesday",
  "Thursday",
  "Friday",
  "Saturday",
  "Sunday"
];

final positions = weekDays.asMap().map((ind, day) => MapEntry(day, ind));

The positions is slightly more interesting; by calling asMap, I’m converting the list to a map with the keys being the positions (i.e. 0:"Monday", … 6:"Friday") and then swapping them. This will result in a slightly faster lookup than just using indexOf, although that’s realistically probably an unnecessary optimization in this case.

Then to sort, you can just use a list’s sort method and pass it a custom comparitor function:

dates.sort((first, second) {
  final firstPos = positions[first] ?? 7;
  final secondPos = positions[second] ?? 7;
  return firstPos.compareTo(secondPos);
});

Putting it all together, this is what it looks like:

const weekDays = [
  "Monday",
  "Tuesday",
  "Wednesday",
  "Thursday",
  "Friday",
  "Saturday",
  "Sunday"
];

final positions = weekDays.asMap().map((ind, day) => MapEntry(day, ind));

void main() {
  final dates = ["Friday", "Monday", "Sunday", "Banana", "Wednesday"];

  dates.sort((first, second) {
    final firstPos = positions[first] ?? 8;
    final secondPos = positions[second] ?? 8;
    return firstPos.compareTo(secondPos);
  });
  
  print("sorted: $dates");
}

Note that if your data isn’t complete sanitized, you might want to normalize it to be all lower case, and do the same for your "weekDays" listing.