Generate List of total sales for similar date from another list that has repeated days

Question

I have a list of daily sales which includes "DateTime" & "Int" for each entry. The issue with this list is that there are some times multiple entries for the same date.

final data = [
      DailySales(2022-03-10 05:25:40.000, 200),
      DailySales(2022-03-10 09:10:50.000, 455),
      DailySales(2022-03-09 04:70:30.000, 255),
      DailySales(2022-03-09 20:10:20.000, 525),
      DailySales(2022-02-08 05:60:00.000, 100),
      DailySales(2022-02-10 00:00:00.000, 520),
      DailySales(2022-01-08 12:10:40.000, 100),
      DailySales(2022-01-08 02:30:10.000, 250),
      DailySales(2022-01-10 09:20:00.000, 520),
    ];

class DailySales {
  final DateTime day;
  final int sales;

  DailySales(this.day, this.sales);
}

Now Based on the above list, I need to dynamically generate a new list that combine the sales in one entry if there is multiple entries of similar date. i.e one entry per date and the total sales for that date.

Answer 1

A basic workaround:

I'll be implementing a simple technique on the sample data from your question.

Your data:

final data = [
    DailySales(2022-03-10 00:00:00.000, 200),
    DailySales(2022-03-10 00:00:00.000, 455),
    DailySales(2022-03-09 00:00:00.000, 255),
    DailySales(2022-03-09 00:00:00.000, 525),
    DailySales(2022-02-08 00:00:00.000, 100),
    DailySales(2022-02-10 00:00:00.000, 520),
    DailySales(2022-01-08 00:00:00.000, 100),
    DailySales(2022-01-08 00:00:00.000, 250),
    DailySales(2022-01-10 00:00:00.000, 520),
];

You need to add all the Objects with same date like:

void processData() {
  List<DailySales> processedData = [];

  for (var dailySales in data) {
    int sales = 0;

    final dailyFormat = DateFormat("dd-MM-yyyy").format(dailySales.day);
    
    for (int i = 0; i < data.length; i++) {

      final dateFromData = DateFormat("dd-MM-yyyy").format(data[i].day);

      if (dateFromData == dailyFormat) {
        sales += data[i].sales;
      }
    }

    processedData
        .add(DailySales(DateFormat("dd-MM-yyyy").parse(dailyFormat), sales));
    
  }
  
  final Map<DateTime, DailySales> map = {
    for (var dailySales in processedData) dailySales.day : dailySales,  
  };
  
  processedData = map.values.toList();
}

The list named processedData will contain DailySales with one entry for each date.

Update: You need to use intl package for this.

Answer 2

for(int i=0; i<data.length;i++){

 if(finalList.contains(data[i].day) {
   final tempSales=finalList.firstWhere((element)=>element.day==data[i].day)
   data[i].sales+= tempSales.sales
  }
   else{
     finalList.add(data);
   }
 
 }