Reassigning dictionary elements through loop

Question

I have a Dictionary. I've used a loop to add elements in the dictionary and changed them over time through code. How can I revert the elements back to their initial value? My code:

//for adding to the dictionary
Dictionary<string, string> D = new Dictionary<string, string>();

for(i=0; i<DataSet1.Tables[0].Rows.Count; i++)
{
    row = DataSet1.Tables[0].Rows[i];
    id[i]=row["UserID"].ToString(); 

    D.Add(id[i], "absent");
}   

//for reassigning back to absent
for(int i =0; i<D.Count; i++) D[i.ToString()]="absent";

My reassigning loop instead of reassign seems to just add new elements. Initialy counted about 1000 and after the reassign loop it's about 3000.. P.S. Using c# Please help

Answer 1

Give this a try:

foreach(var key in d.Keys.ToArray())
{
    d[key] = "absent";
}

The .ToArray() is needed because the foreach loop will throw an error before the second iteration if you try to iterate on d.Keys directly.

Answer 2

You can enumerate keys of your dictionary and set entries values:

foreach(string key in D.Keys.ToArray())
    D[key] = "absent";

Also creation of dictionary can be simplified to (with help of Linq to DataSet):

var D = DataSet1.Tables[0].AsEnumerable()
                .ToDictionary(r => r.Field<string>("UserID"),
                              r => "absent");