将缺少的值添加到xamarin表单中的列表中

Question

I have a custom object list which has month and another int value. I am getting this list from the database. So data coming from a web service as JSON. Sometimes month is not consecutive. Sometimes some month get missing. For example if this is month 7,

then months in list may contains something like this. {1,2,3,6,7}

so I want to add the missing months which are 4,5 ---- {1,2,3,4,5,6,7}

other value should be 0 (NEW_REC_COUNT)

My Object class

public class NewData
{
    public int MONTH { get; set; }
    public int NEW_REC_COUNT { get; set; }
}

Sample Json

[
    {
        "MONTH": 1,
        "NEW_REC_COUNT": 19
    },
    {
        "MONTH": 2,
        "NEW_REC_COUNT": 5
    },
    {
        "MONTH": 3,
        "NEW_REC_COUNT": 2
    },
    {
        "MONTH": 6,
        "NEW_REC_COUNT": 9
    },
    {
        "MONTH": 7,
        "NEW_REC_COUNT": 3
    }
]

Answer 1

You can try below approach,

1. Select all months (int value) from list using Select

     var months = NewDataList.Select(x => x.MONTH); // This will give you all integers ie MONTHs. 

2. Find Max() from months and create Range from 1... maxMonths

    var maxMonths = months.Max(); var oneTomaxMonths = Enumerable.Range(1,maxMonths).ToList(); 

Now you have 2 lists ie months and oneToMaxMonths , use Except to get missing Months from list of New Data

var results = oneTomaxMonths.Except(months);

Foreach result create new instance with NEW_REC_COUNT = 0

POC : .net Fiddle

Answer 2

If you don't have a lot of data, you can try a smiple loop and Insert omitted items into the list:

List<NewData> list = ...

// If list is not guarantee to be sorted
list.Sort((a, b) => a.MONTH.CompareTo(b.MONTH));

for (int i = 0; i < list.Count - 1; ++i) {
  NewData current = list[i];
  NewData next = list[i + 1];     

  // Do we have a hole at position i + 1? 
  if (current.MONTH + 1 < next.MONTH) {
    list.Insert(i + 1, new NewData() {
      MONTH = current.MONTH + 1,  // Omitted month
      NEW_REC_COUNT = 0,          // Default value
    });
  }
}

Edit: If we want months from 1 up and including the current month ( DateTime.Today.Month ), we can use Linq :

  using System.Linq;

  ...

  List<NewData> list = ...

  // Let's generalize a bit if you want, say Q3 period
  int fromMonth = 1;
  int upToMonth = DateTime.Today.Month; // or 7 for testing

  list = Enumerable
    .Range(fromMonth, upToMonth - fromMonth + 1)
    .Select(month =>
          list.FirstOrDefault(item => item.MONTH == month)
       ?? new NewData() { MONTH = month,       // Omitted month 
                          NEW_REC_COUNT = 0 }) // Default value
    .ToList();

If you want to modify existing list :

  list.AddRange(Enumerable
    .Range(fromMonth, upToMonth - fromMonth + 1)
    .Where(month => !list.Any(item => item.MONTH == month))
    .Select(month => new NewData() { 
       MONTH = month, 
       NEW_REC_COUNT = 0 })
    .ToArray());