# IListT Extension Method Example Comparing 2 Lists

You can use the following extension method for comparing the contents of two IList< T > instances of the same type.

By default the items are compared based on their order within the list and the items themselves, passing false to the `isOrdered` parameter will compare only the items themselves regardless of their order.

For this method to work, the generic type (`T`) must override both `Equals` and `GetHashCode` methods.

Usage:

```List<string> list1 = new List<string> {"a1", "a2", null, "a3"};
List<string> list2 = new List<string> {"a1", "a2", "a3", null};

list1.Compare(list2);//this gives false
list1.Compare(list2, false);//this gives true. they are equal when the order is disregarded```

Method:

```public static bool Compare<T>(this IList<T> list1, IList<T> list2, bool isOrdered = true)
{
if (list1 == null && list2 == null)
return true;
if (list1 == null || list2 == null || list1.Count != list2.Count)
return false;

if (isOrdered)
{
for (int i = 0; i < list2.Count; i++)
{
var l1 = list1[i];
var l2 = list2[i];
if (
(l1 == null && l2 != null) ||
(l1 != null && l2 == null) ||
(!l1.Equals(l2)))
{
return false;
}
}
return true;
}
else
{
List<T> list2Copy = new List<T>(list2);
//Can be done with Dictionary without O(n^2)
for (int i = 0; i < list1.Count; i++)
{
if (!list2Copy.Remove(list1[i]))
return false;
}
return true;
}
}```

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