Delete all the keys from the dictionary if the value matches for more than one key

Question

I have a dictionary

private readonly Dictionary<string, WebResponse> _myDictionary;

Lets assume I have 10 values in the dictionary currently. I can able to add some values into it also I can delete the values based on the key present in the dictionary similar to below.

Remove:

_myDictionary.Remove(Key);

where key is a string variable.

Is that possible to delete more than one key at a time if the values matches for more than one key. I have keys like {KAAR1, KAAR2, KAAR3, ABCDEF}. Now I need to delete all the keys which contains "KAAR". Is that possible to do.

Kindly help.

Try this: `_myDictionary.Where(x => x.Key.Contains("KAAR")).ToList().ForEach(kvp => _myDictionary.Remove(kvp.Key));`. — Enigmativity, Jul 17 '18 at 06:24
@Enigmativity why don't you add this as answer. It looks a pretty good idea to me — Ahmad, Jul 17 '18 at 06:29
Check this question for more ways to do the same https://stackoverflow.com/questions/469202/best-way-to-remove-multiple-items-matching-a-predicate-from-a-c-sharp-dictionary — Karan, Jul 17 '18 at 06:33
@Enigmativity - Your answer worked without any problem. Thank you very much! — Priya, Jul 17 '18 at 07:08

score 9 · Answer 1 · answered Jul 17 '18 at 06:30

9

Try this:

_myDictionary
    .Where(x => x.Key.Contains("KAAR"))
    .ToList()
    .ForEach(kvp => _myDictionary.Remove(kvp.Key));

answered Jul 17 '18 at 06:30

Enigmativity

113,464
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172

Why `ToList()`? – Chayim Friedman Jul 17 '18 at 06:51
@חייםפרידמן Probably because this way it doesn't create a *new* Dictionary – Fabjan Jul 17 '18 at 06:56
1

@חייםפרידמן Because where outputs in IEnumerable on which we can't apply Foreach loop. Thats why it is needed to convert to LIST. – Ahmad Jul 17 '18 at 06:59
@חייםפרידמן - The `.ToList()` call also forces the full enumeration of the dictionary so that the `.Remove(...)` calls won't change the dictionary while enumerating. And, as Ahmad says, to get access to the `.ForEach(...)` extension method. – Enigmativity Jul 17 '18 at 07:12
Thanks. I undestand. – Chayim Friedman Jul 17 '18 at 07:19
A small hint: Using extension methods are highly beneficial for lists and dictionaries because it allows the use of syntax like this: `ListObj.YourMethod ();` And the question seems to demand a general solution applicable for generic types. – Battle Jul 17 '18 at 08:25
@Battle - Sorry, I don't understand. What do you mean by `ListObj.YourMethod();`? – Enigmativity Jul 17 '18 at 11:58
@Enigmativity - It wasn't directed at you personally, and was not meant as any criticism - your answer is great. I just wanted to point out that all of that can be wrapped into an extension method using generics... and with the answer below I also added the code for it. – Battle Jul 17 '18 at 12:13

score 0 · Accepted Answer · answered Jul 17 '18 at 07:36

0

Below is the answer given by the user @Enigmavitivity!! Added as seprate answer to mark as a correct one.

_myDictionary.Where(x => x.Key.Contains("KAAR")).ToList().ForEach(kvp => _myDictionary.Remove(kvp.Key));

answered Jul 17 '18 at 07:36

Priya

69
5

Battle · Answer 3 · 2018-07-17T09:45:56.273

I expanded the answer of @Enigmativity to provide two generic versions as extension methods.

/// <summary> Removes all duplicate values after the first occurrence. </summary>
public static void RemoveDuplicates<T, V> (this Dictionary<T, V> dict)
{
    List<V> L = new List<V> ();
    int i = 0;
    while (i < dict.Count)
    {
        KeyValuePair<T, V> p = dict.ElementAt (i);
        if (!L.Contains (p.Value))
        {
            L.Add (p.Value);
            i++;
        }
        else
        {
            dict.Remove (p.Key);
        }
    }
}

With a dictionary of values (ignoring keys): 0, 1, 2, 3, 5, 1, 2, 4, 5. Result: 0, 1, 2, 3, 5, 4.

/// <summary> Removes all values which have any duplicates. </summary>
public static void RemoveAllDuplicates<T, V> (this Dictionary<T, V> dict)
{
    List<V> L = new List<V> ();
    int i = 0;
    while (i < dict.Count)
    {
        KeyValuePair<T, V> p = dict.ElementAt (i);
        if (!L.Contains (p.Value))
        {
            L.Add (p.Value);
            i++;
        }
        else
        {
            dict.Where (j => Equals (j.Value, p.Value)).ToList ().ForEach (j => dict.Remove (j.Key));
        }
    }
}

With a dictionary of values (ignoring keys): 0, 1, 2, 3, 5, 1, 2, 4, 5. Result: 3, 4.

The methods are optimized to prevent multiple executions of the .Where operation (otherwise each duplicate would have n executions of it, where all after the first one is obsolete). Code is tested and working.

Delete all the keys from the dictionary if the value matches for more than one key

3 Answers3