一次从字典中删除多个项目

Question

I have a dictionary like so:

Dictionary<KeyValuePair<int, string>, OperationType> clickedList;

where OperationType is an Enum { Download, Install, Remove, Enable }

I have another KeyValuePair list like so:

toRemove = machine.Array
                  .Select(x => 
                      new KeyValuePair<int, string>((int)x.MachineID, x.PackageID))
                  .ToList();

I need to do the following:

1. Remove all items from clickedList that exist in toRemove and OperationType != "Remove"
2. Remove all items from clickedList that have OperationType = "Remove" and DO NOT exist in toRemove list.

Is there a good way of doing this? How would I do it?

Answer 1

I would think that the most efficient way to do that would be to use a HashSet> to store all the keys that should actually be removed from the dictionary - although this solution doesn't use linq:

toRemove = machine.Array
              .Select(x => 
                  new KeyValuePair<int, string>((int)x.MachineID, x.PackageID))
              .ToList();

// create a hash set and initially put all the elements from toRemove in the set
var r = new HashSet<KeyValuePair<int, string>>(toRemove);

// go over each element in the clickedList
//    and check whether it actually needs to be removed
foreach(var kvp in clickedList.Keys)      // O(n);  n = # of keys/elem. in dictionary
{
    if(kvp.Value == OperationType.Remove)
    {
       if(r.Contains(kvp.Key)             // O(1)
          r.Remove(kvp.Key);              //    (1)
       else
          r.Add(kvp.Key);                 //   O(1)
    }
}

foreach(var key in r)                     // O(m); m = # of keys to be removed 
{
    clickedList.Remove(key);
}

I believe the above is probably the most efficient way of removing the elements since it's linear in the number of keys in the dictionary.