Filtering out values from a C# Generic Dictionary

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If you don’t care about creating a new dictionary with the desired items and throwing away the old one, simply try:

dic = dic.Where(i => i.Value.BooleanProperty)
         .ToDictionary(i => i.Key, i => i.Value);

If you can’t create a new dictionary and need to alter the old one for some reason (like when it’s externally referenced and you can’t update all the references:

foreach (var item in dic.Where(item => !item.Value.BooleanProperty).ToList())
    dic.Remove(item.Key);

Note that ToList is necessary here since you’re modifying the underlying collection. If you change the underlying collection, the enumerator working on it to query the values will be unusable and will throw an exception in the next loop iteration. ToList caches the values before altering the dictionary at all.

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