Operator '==' cannot be applied to operands of type 'TValue' and 'TValue'

Question

I need to find the index of a particular item with TValue list using Linq methods without using looping. I have tried to find index by comparing single TValue with a IEnumerable collection of Tvalue like below code

 int idx= list.Select((elem, index) => new { elem, index }).First(p => p.elem == item).index;

With this, I am getting the following error

CS0019 Operator '==' cannot be applied to operands of type 'TValue' and 'TValue'

I have also tried Equals with this code but that too doesn't return exact index value.

 int idx= list.Select((elem, index) => new { elem, index }).First(p => p.elem.Equals(item)).index;

Here, the list is a collection of TValue with 5 items and item is a TValue with a single item whose index is to be found within the list. Find the structure in below image

Please suggest a way to find index by comparing both TValue

Regards,

Keerthana.

Answer 1

Not everything can be compared directly. For example

var item1 = new KeyValuePair<int, string>(1, "text");
var item2 = new KeyValuePair<int, string>(1, "text");

var theSame = (item1 == item2);

would give an error of

CS0019 Operator '==' cannot be applied to operands of type 'KeyValuePair<int, string>' and 'KeyValuePair<int, string>'

So, if you can't compare one TValue with another, then you may need to compare each element individually, ie

 int idx= list.Select((elem, index) => new { elem, index })
         .First(p => p.elem.Id == item.Id && p.elem.Text == item.Text).index;

Answer 2

You can try the this code

int idx= list.Select((elem, index) => new { elem, index }).First(p => EqualityComparer.Default.Equals(p.elem item).index