How to sort List<Map<String, dynamic>> by timestamp in flutter?

Question

I am building a list of data of type List<Map<String, dynamic>> (which I am getting from firebase documents all of which have the following data: document fields). Once I get all the data I would like to sort the list by the createdOn field (which is a timestamp) but I'm unsure as to how to sort it. Here's a snippet of code showing how I build the list:

Future<List<Map<String, dynamic>>>? getData(List<String> subcategory) async {
    List<Map<String, dynamic>> allData = [];
    try {
      String? email = FirebaseAuth.instance.currentUser!.email;
      var categories = Utils.categoriesDropdownItems;
      for (var i = 0; i < subcategory.length; ++i) {
        var doc = await FirebaseFirestore.instance
            .collection(email!)
            .doc(categories[0])
            .collection(subcategory[i])
            .get();
        allData.addAll(doc.docs.map((doc) => doc.data()).toList());
      }
      allData.sort(); //Unsure how to approach sorting by timestamp??

I'm unsure how to extract the created on field to be able to sort it. I tried doing something like:

allData.sort((a, b) => a["cretedOn"].compareTo(b["createdOn"]));

but it seems like compareTo does not exist for a["createdOn"]?

FlutterBuilder · Accepted Answer · 2023-01-02 22:08:32Z

3

Solved. I just had to make sure the timestamps were defined as follows:

allData.sort(((a, b) {
    Timestamp one = a["createdOn"];
    Timestamp two = b["createdOn"];
    return two.compareTo(one);
  }));

answered Jan 2, 2023 at 22:08

FlutterBuilder

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Comments

Ahmed Khattab · Accepted Answer · 2023-01-03 00:55:01Z

0

You can order them directly in your firestore query using orderBy like this

.collection(subcategory[i]).orderBy('createdOn', descending: true);

answered Jan 3, 2023 at 0:55

Ahmed Khattab

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Comments

Mohammad Ali · Accepted Answer · 2023-12-14 12:20:43Z

0

You can use the sort method with a custom comparison function.

 void main() {
  List<Map<String, dynamic>> data = [
    {'timestamp': 1639791020, 'value': 'Item 1'},
    {'timestamp': 1639794320, 'value': 'Item 2'},
    {'timestamp': 1639792120, 'value': 'Item 3'},
    // Add more items as needed
  ];

  // Sorting the list based on the 'timestamp' field in descending order
  data.sort((a, b) => b['timestamp'].compareTo(a['timestamp']));

  // Printing the sorted list
  print(data);
}

I hope this will help you.

edited Dec 14, 2023 at 12:20

answered Dec 14, 2023 at 12:10

Mohammad Ali

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