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

Question

I have a list of Week Day names in random order, how to sort it in ascending order e.g. Monday, Tuesday, Wednesday …

List

[Friday, Monday, Sunday, Wednesday]

Desired List

[Monday, Wednesday, Friday, Sunday]

I have tried

list.sort((a, b) => a.toLowerCase().compareTo(b.toLowerCase()));

Answer 1

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.