C＃中动态列表数的比较

Question

I have a variable number of List-objects, of which I need to compare the values at the same indexes. The number of entries in the list is given and does not vary.

For example: 4 Lists each 4 entries

So what I'd be looking for in this example, is 4 bools, one per index. Getting the indexes of unmatching entries would be fine, too.

Pseudo:

bool isFirstEqual = (list1[i] == list2[i] == list3[i] == list4[i]);

But I need to do this in a fashion that's applicable for a variable number of lists. I could have 6 Lists, but also 2.

I was thinking of doing something with LINQs .Except() but am not sure how to use it with a variable number of lists.

I am struggling to find the elegant solution that I'm sure is out there. Any help on this is appreciated.

Answer 1

If i understand what you mean, something like this might work

public static bool IsEqual<T>(int index, params List<T>[] ary)
{
   for (var i = 1; i < ary.Length; i++)
      if (!EqualityComparer<T>.Default.Equals(ary[0][index], ary[i][index]))
         return false;         

   return true;
}

Usage

var isSecondelemEqual = IsEqual(1, list1, list2, list3,...)

Update

Basically takes a variable list of lists, and assumes you want to check the index of each list against each other.

Answer 2

bool AreIndexesEqual(int index, List<List<int>> lists)
{
    int match = lists[0][index];

    foreach(List<int> list in lists.Skip(1))
    {
        if (list[index] != match)
        {
            return false;
        }
    }

    return true;
}

Answer 3

Given for example:

List<List<int>> listOfLists = new List<List<int>>
{
    new List<int> { 1, 100, 2},
    new List<int> { 2, 100, 3},
    new List<int> { 3, 100, 4},
    new List<int> { 4, 100, 5},
};

So a List<> of List<int>

the totally unreadable LINQ expression that will return a List<bool> is something like:

List<bool> result = Enumerable.Range(0, listOfLists.Count != 0 ? listOfLists[0].Count : 0)
            .Select(x => listOfLists.Count <= 1 ? 
                true : 
                listOfLists.Skip(1).All(y => y[x] == listOfLists[0][x])
            ).ToList();

Here I want to show you that if your first solution to any problem is LINQ, then perhaps now you will have two problems.

Now... What does this linq does? We have 4 List<int> , each one with 3 elements... So 3 rows of 4 columns. We want to calculate the result "by row", so the first thing is discover the number of rows, that is listOfLists[0].Count (we put a pre-check for the case that we have 0 rows). Now we generate an index (like a for ), using Enumerable.Range(0, numberofrows) , like for (int i = 0; i < numberofrows; i++) . For each row we see if there are 0 or 1 columns ( listOfLists.Count <= 1 ), then the result is true , otherwise we compare all the other columns y[x] with the first column listOfLists[0][x] .

With a dual for cycle it becomes clearer probably:

var result2 = new List<bool>(listOfLists.Count != 0 ? listOfLists[0].Count : 0);

// Note the use of .Capacity here. It is listOfLists.Count != 0 ? listOfLists[0].Count : 0
for (int col = 0; col < result2.Capacity; col++)
{
    if (listOfLists.Count <= 1)
    {
        result2.Add(true);
    }
    else
    {
        bool equal = true;

        for (int row = 1; row < listOfLists.Count; row++)
        {
            if (listOfLists[row][col] != listOfLists[0][col])
            {
                equal = false;
                break;
            }
        }

        result2.Add(equal);
    }
}

Note that both programs can be simplified: new int[0].All(x => something) == true , so .All() on empty IEnumerable<> is true . You can remove listOfLists.Count <= 1 ? true : listOfLists.Count <= 1 ? true : and if (...) { ... } else up to the else keyword, keeping only the code inside the else :

var result2 = new List<bool>(listOfLists.Count != 0 ? listOfLists[0].Count : 0);

// Note the use of .Capacity here. It is listOfLists.Count != 0 ? listOfLists[0].Count : 0
for (int col = 0; col < result2.Capacity; col++)
{
    bool equal = true;

    for (int row = 1; row < listOfLists.Count; row++)
    {
        if (listOfLists[row][col] != listOfLists[0][col])
        {
            equal = false;
            break;
        }
    }

    result2.Add(equal);

}

Answer 4

Here you go

IEnumerable<bool> CompareAll<T>(IEnumerable<IEnumerable<T>> source)
{
    var lists = source.ToList();
    var firstList = lists[0];
    var otherLists = lists.Skip(1).ToList();

    foreach(var t1 in firstList)
    {
        yield return otherlists.All(tn => tn.Equals(t1));
    }
}