Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

I'm currently working on a C# 4.7.2 application. I'm about to write an extension method for a custom type and I'm struggling with my LINQ query unfortunately.

I need filter a List<Dictionary<string, object>> to find the elements of Dictionary<string, object> in the list with a certain key and remove it from my list. Furthermore, a list entry can be null.

A list entry (dictionary) can look like this, there can be several elements with value key A, i need to remove all actually:

Key    |  Value
"MyId" : "A",
"Width" : 100,
"Length" : 50
Very simple structure. The tricky thing is to find the dictionary elements in the list. My extension method looks like that:
public static List<Dictionary<string, object>> RemoveItem(this List<Dictionary<string, object> items, string value)
    var itemToRemove = items.FirstOrDefault(x => x.ContainsKey("MyId")).Values.Contains(value);
    items.Remove(itemToRemove);
    return items;
Unfortunately this LINQ query does not work correctly.
Do you know how to solve this issue?
Thank you very much!!
                "Does not work" has never been a suiteable problem description on a programming forum. Please tell us what exactly is happening or not happening.
– Christopher
                Nov 15, 2018 at 9:13
                Hi sorry, actually I need to remove all dictionary items from the list, that have the key MyId and it's value A, let's say...
– timhorton42
                Nov 15, 2018 at 9:14
You want to remove all with a key and a value? You don't even need LINQ:
public static int RemoveItems(this List<Dictionary<string, object>> dictionaryList, string value)
    int removed = dictionaryList
        .RemoveAll(dict => dict.TryGetValue("MyId", out object val) && value.Equals(val));
    return removed;
You could use the method RemoveAll of the list. Then you give in a predicate that checks the dictionary (which is a collection of KeyValuePair<TKey, TValue>):
items.RemoveAll(dict => dict.Any(kv => kv.Key == "MyId" && ( kv.Value as string ) == "A"));
Or as suggested by Tim Schmelter:
items.RemoveAll(dict => dict.TryGetValue("MyId", out object value) && (value as string) == "A");
                well, if you use a dictionary then mostly because retrieving a value by using its key is very fast(O(1)).
– Tim Schmelter
                Nov 15, 2018 at 9:29
From your description, you seem to want the first dictionary containing the key with the value from the parameter value. That would be items.FirstOrDefault(x => x.ContainsKey(value))
What you are doing is getting dictionary containing one predefined key "myId" and then going through the objects inside the dictionary and comparing their values with your value parameter, which is not what you described you want.
If you expect more dictionaries to contain the given key,and you want to remove all of them, you should use list.RemoveAll(dict => dict.ContainsKey(value))
public static List<Dictionary<string, object>> RemoveItem(this List<Dictionary<string, object>> items, string value, string key)
    foreach (var item in items)
        if(item.ContainsKey(key) && item[key] == value)
            item.Remove(key);
    return items;
This gonna work just fine.
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.