C#：从列表中选择特定的索引值

Question

I am looking for a way to search a list that returns me an bunch of indexes based on a search i make on that list. For ex i have a comma separated string list as follows:

Blue, 3
Red, 3
Blue, 1
Blue, 9
Red, 5

I want to make a search that returns me indexes of all elements EXCEPT any that contain the text found in a criteria list. The criteria list could contain:

Blue, 3
Red, 5

So in pseudo code, it would be,

ColorList.SelectIndex(!Containing(Words found in all elements of criteriaList)

The above should return indexes 1,2,3

Thanks

Answer 1

var indexes = ColorList.Select((x, i) => new { Value = x, Index = i })
                       .Where(x => !criteriaList.Contains(x.Value))
                       .Select(x => x.Index);

If your lists contain many items then you might get better performance by converting criteriaList to a HashSet<T> first. (You'll need to benchmark to determine whether this is the better option in your case.)

var criteriaSet = new HashSet<string>(criteriaList);
var indexes = ColorList.Select((x, i) => new { Value = x, Index = i })
                       .Where(x => !criteriaSet.Contains(x.Value))
                       .Select(x => x.Index);

Answer 2

var list = new []{"Blue, 3", "Red, 3", "Blue, 1", "Blue, 9", "Red, 5"};
var criteria = new []{"Blue, 3", "Red, 5"};

var filtered = list
        .Select((s,i)=>new {s,i})
        .Where(e => !criteria.Contains(e.s))
        .Select(e => e.i);

results: { 1, 2, 3 }

Answer 3

void Main()
{
    var data = new List<string> {"Blue, 3", "Red, 3", "Blue, 1", "Blue, 9", "Red, 5"};

    var colorList = new List<string> {"Blue, 3", "Red, 5"};

    var indexes = data.Except(colorList).Select (x => data.IndexOf(x));

    indexes.Dump();
}

Answer 4

Sounds like you may want to use a

 List<KeyValuePair<string, int>> pair = new KeyValuePair<string, int>

then you can do

foreach (KeyValuePair<string, int> p in pair){
    s = p.Key;
    i = p.Value;
}

to get the values

Answer 5

I am not quite sure what you want to achieve here, so perhaps my answer is not what you are looking for.

Anyway, in a generic list, you could use a lambda expression/ linq statement on your collection. Consider these examples I have written for you:

internal class ListLambdaLINQSample
{

    List<KeyValuePair<Colors, int>> listSource;
    List<KeyValuePair<Colors, int>> listCriteria;
    List<KeyValuePair<Colors, int>> listMatches;

    private const int COLORCODE1 = 1;
    private const int COLORCODE2 = 2;
    private const int COLORCODE3 = 3;
    private const int COLORCODE4 = 4;
    private const int COLORCODE5 = 5;

    internal enum Colors
    {
        Red, Blue, Green, Yellow
    }


    public ListLambdaLINQSample()
    {   // populate the list
        listSource = new List<KeyValuePair<Colors, int>>();
        listCriteria = new List<KeyValuePair<Colors, int>>();

        _populateListCriteria();
        _populateListSource();

        ...
    }

    private void _getMatchesWithLINQ()
    {
        listMatches =
                        (from kvpInList
                             in listSource
                         where !listCriteria.Contains(kvpInList)
                         select kvpInList).ToList();
    }

    private void _getMatchesWithLambda()
    {
        listMatches =
            listSource.Where(kvpInList => !listCriteria.Contains(kvpInList)).ToList();
    }


    private void _populateListSource()
    {
        listSource.Add(new KeyValuePair<Colors, int>(Colors.Blue, COLORCODE1));
        listSource.Add(new KeyValuePair<Colors, int>(Colors.Green, COLORCODE2));
        listSource.Add(new KeyValuePair<Colors, int>(Colors.Red, COLORCODE3));
        listSource.Add(new KeyValuePair<Colors, int>(Colors.Yellow, COLORCODE4));
    }

    private void _populateListCriteria()
    {
        listCriteria.Add(new KeyValuePair<Colors, int>(Colors.Blue, COLORCODE1));
        listCriteria.Add(new KeyValuePair<Colors, int>(Colors.Green, COLORCODE2));
    }
}

Hope this helps!!

Regards, Nico

PS: I haven't compiled nor tested this code.