How to sort a List<String> of formatted dates in dart?

Question

I have tried this on dartpad,

void main() {
  final List<String> dates=["24-06-2021","27-05-2021","21-04-2021","29-07-2021","15-12-2021"];
  var sorted = dates..sort((a,b) => a.compareTo(b));
  print(sorted);
}

Output : [15-12-2021, 21-04-2021, 24-06-2021, 27-05-2021, 29-07-2021]
Desired : [21-04-2021, 27-05-2021, 24-06-2021, 29-07-2021, 15-12-2021]

Any help is appreciated.

an hour ago i gave you a solution with integers, the same works with DateTime objects — pskink
– pskink, Commented Jun 7, 2021 at 5:37
This code works, ` void main() { final List<String> dates=["2021-06-24","2021-05-24"]; var sorted = dates.map(DateTime.parse).toList()..sort((a,b) => a.compareTo(b)); for(int i =0;i<sorted.length;i++){ String date = '${sorted[i].day}-${sorted[i].month}-${sorted[i].year}'; print(date); } } ` but is it efficient. @pskink — Vinay Saurabh
– Vinay Saurabh, Commented Jun 7, 2021 at 6:00
That's as efficient as you can get. You can't do a comparison-based sort faster than O(n log n), and converting everything to DateTime objects first means that you don't need to reparse the same strings when performing multiple comparisons of the same element. — jamesdlin
– jamesdlin, Commented Jun 7, 2021 at 7:46

Giorgi · Accepted Answer · 2021-06-07 06:33:56Z

1

import 'package:intl/intl.dart';


 List dates = ["24-06-2021",
                  "27-05-2021",
                  "21-04-2021",
                  "29-07-2021",
                  "15-12-2021"];

  List<DateTime> newdates = [];
  DateFormat format = DateFormat("dd-MM-yyyy");

  for (int i = 0; i < dates.length; i++) {
    newdates.add(format.parse(dates[i]));
  }
  newdates.sort((a,b) => a.compareTo(b));

  for (int i = 0; i < dates.length; i++) {
    print(newdates[i]);
  }

edited Jun 7, 2021 at 6:33

answered Jun 7, 2021 at 6:12

Giorgi

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2 Comments

Alex Radzishevsky Over a year ago

Date format needs to be fixed to dd-MM-yyyy

Vinay Saurabh Over a year ago

Thanks guys, have tweaked it a little bit and finally got my code.

Vinay Saurabh · Accepted Answer · 2021-06-08 11:51:03Z

0

import 'package:intl/intl.dart';

List<String> getSortedDates(List<String> dates){

  //Formatting for acceptable DateTime format
  DateFormat formatter = DateFormat("dd-MM-yyyy");

  //Mapping to convert into appropriate dateFormat
  List<DateTime> _formattedDates = dates.map(formatter.parse).toList();
  
  //Apply sort function on formatted dates
  _formattedDates.sort();

  //Mapping through sorted dates to return a List<String> with same formatting as passed List's elements
  return _formattedDates.map(formatter.format).toList();

}

edited Jun 8, 2021 at 11:51

answered Jun 7, 2021 at 7:56

Vinay Saurabh

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