按通用值排序字典

Question

I have tried to sort a Dictionary object by value which is generic.

Here is my code

Dictionary<string, ReportModel> sortedDic = new Dictionary<string, ReportModel>();
Dictionary<string, ReportModel> rDic = new Dictionary<string, ReportModel>();
var ordered = sortedDic.OrderByDescending(x => x.Value.totalPurchase);
foreach (var item in ordered)
{                           
    rDic.Add(item.Key, item.Value);
}

The variable, ordered, just has the same order like sortedDic. What is wrong with this? Any idea?

Answer 1

This happens because Dictionary is generally an unordered container ^* . When you put the data into rDic , it becomes unordered again.

To retain the desired order, you need to put the results into a container that explicitly keeps the ordering that you supply. For example, you could use a list of KeyValuePair<string,ReportModel> , like this:

IList<KeyValuePair<string,ReportModel>> ordered = sortedDic
    .OrderByDescending(x => x.Value.totalPurchase)
    .ToList();

---

^* Due to the way the Dictionary<K,V> is implemented by Microsoft, it happens to retain the insertion order , but that is incidental and undocumented, so it may change in the future versions, and should not be relied upon.

Answer 2

When adding the items back to the dictionary, it would not keep their order. You can either:

1. Use the following implementation .

2. Use a list in the below form.

    IEnumrable> lst= \n   sortedDic.OrderByDescending(x => x.Value.totalPurchase).ToArray();  

3. [EDIT] If you don't mind the key changing then you can use SortedDictionary<,>.