比较列表中的每个项目与另一个列表中的另一个项目

Question

I have 2 list of double

List<double> numbers1 = [1,3,5,6,4.5,2.1,.......];
List<double> numbers2 = [.5,3.2,5.4,6,4.5,2.1,.......];

I want to compare [1] in list1 whith [.5] in list 2

if([1] close to[.5]) for example

which means if the first item value in fisrst list close to the first item value in second list and etc, the second with second, third with third

How can I do this c#?

Answer 1

Simply check for the difference between two related items using Math.Abs :

bool allElementsClose = true;
for(int i = 0; i < lis1.Count && allElementsClose; i++)
{
    if(Math.Abs(list1[i] - list2[i]) > threshold) 
    {
        Console.WiteLine("items not close");
        allElementsClose = false;
        break;
    }
}

You should however make some checks on the number of items before iterating.

Alternative approach using LINQ:

var allElementsClose = list1
    .Select((x, i) => Math.Abs(x - list2[i]))
    .All(x => x < threashhold);

This approach uses the overload of select that uses a Func<T, int> for getting the element and its index within the collection. This index can then be used to get the appropriate item in the second list and calculate the difference to it.

Answer 2

Simplest solution would be using Zip , which is meant for comparison of each mapping element of two collections and will also take care of difference in number of elements, as it checks the Enumerator.MoveNext() internally

var result = numbers1.Zip(numbers2,(n1,n2) => n1 - n2 < 0.5 ? "Close" : "Not Close");

result would IEnumerable<string> consisting of values "Close" and "Not Close"

Caveat:

• Your question has good number of details missing, as I am not sure what is "Close" and what is "Not Close", I have assumed less than 0.5 difference between two numbers is close, modify as per requirement

Answer 3

Actually it depends on what "close" means for you. I will assume that if the difference between the numbers is less than 1, it is close.

So the code will be really simple

I will create 3 lists. list1, list2, listResult (which will only contain Boolean values, that indicates whether the item in list1 is close to the item in list2.

var list1 = new List<float>();
var list2 = new List<float>();
var listResult = new List<bool>();

The 3 lines above, should go outside the method or event, like button1_click.

//to add values to the list you can use list1.addNew(5) and it will add the "5" to the list

void CompareLists(){
    //first of all we check if list1 and list2 have the same number of items
    if(list1.Count == list2.Count){
        for (int i=0; i<list1.Count; i++){                
            if (list1[i] - list2[i] < 1)
               listResult.addNew(true);
            else
               listResult.addNew(false);
        }
    }
}

Now you have a list of boolens like [true],[true],[false]

Hope, it works for you.

Answer 4

In .Net 4.0 you also have Zip() available:

var numbers1 = new List<double>() { 1, 3, 5, 6, 4.5, 2.1 };
var numbers2 = new List<double>() { 0.5, 3.2, 5.4, 6, 4.5, 2.1 };

var allElementsClose = numbers1
    .Zip(numbers2, (i1, i2) => Math.Abs(i1 - i2))
    .All(x => x < threshold);