SequenceEqual() method is used to determine whether two sequences are equal. This method returns true if the sequences are equal otherwise false.
For 2 sequences to be equal
1. Both the sequences should have same number of elements and
2. Same values should be present in the same order in both the sequences
Example 1 : SequenceEqual() returns true.
string[] countries1 = { "USA", "India", "UK" };
Example 2 : In this case, SequenceEqual() returns false, as the default comparison is case sensitive.
string[] countries1 = { "USA", "INDIA", "UK" };
Example 3: If we want the comparison to be case-insensitive, then use the other overloaded version of SequenceEqual() method to which we can pass an alternate comparer.
string[] countries1 = { "USA", "INDIA", "UK" };
Example 4 : SequenceEqual() returns false. This is because, although both the sequences contain same data, the data is not present in the same order.
string[] countries1 = { "USA", "INDIA", "UK" };
Example 5 : To fix the problem in Example 4, use OrderBy() to sort data in the source sequences.
string[] countries1 = { "USA", "INDIA", "UK" };
Example 6 : When comparing complex types, the default comparer will only check if the object references are equal. So, in this case SequenceEqual() returns false.
List<Employee> list1 = new List<Employee>()
To solve the problem in Example 6, there are 3 ways
1. Use the other overloaded version of SequenceEqual() method to which we can pass a custom class that implements IEqualityComparer
2. Override Equals() and GetHashCode() methods in Employee class
3. Project the properties into a new anonymous type, which overrides Equals() and GetHashCode() methods
We discussed implementing these 3 options for Distinct() method in previous article of LINQ Tutorial. In the same way these options can be implemented for SequenceEqual() method.
For 2 sequences to be equal
1. Both the sequences should have same number of elements and
2. Same values should be present in the same order in both the sequences
Example 1 : SequenceEqual() returns true.
string[] countries1 = { "USA", "India", "UK" };
string[] countries2 = { "USA",
"India", "UK" };
var result = countries1.SequenceEqual(countries2);
Console.WriteLine("Are Equal = " + result);
Example 2 : In this case, SequenceEqual() returns false, as the default comparison is case sensitive.
string[] countries1 = { "USA", "INDIA", "UK" };
string[] countries2 = { "usa",
"india", "uk" };
var result = countries1.SequenceEqual(countries2);
Console.WriteLine("Are Equal = " + result);
Example 3: If we want the comparison to be case-insensitive, then use the other overloaded version of SequenceEqual() method to which we can pass an alternate comparer.
string[] countries1 = { "USA", "INDIA", "UK" };
string[] countries2 = { "usa",
"india", "uk" };
var result = countries1.SequenceEqual(countries2,
StringComparer.OrdinalIgnoreCase);
Console.WriteLine("Are Equal = " + result);
Example 4 : SequenceEqual() returns false. This is because, although both the sequences contain same data, the data is not present in the same order.
string[] countries1 = { "USA", "INDIA", "UK" };
string[] countries2 = { "UK",
"INDIA", "USA" };
var result = countries1.SequenceEqual(countries2);
Console.WriteLine("Are Equal = " + result);
Example 5 : To fix the problem in Example 4, use OrderBy() to sort data in the source sequences.
string[] countries1 = { "USA", "INDIA", "UK" };
string[] countries2 = { "UK",
"INDIA", "USA" };
var result = countries1.OrderBy(c =>
c).SequenceEqual(countries2.OrderBy(c => c));
Console.WriteLine("Are Equal = " + result);
Example 6 : When comparing complex types, the default comparer will only check if the object references are equal. So, in this case SequenceEqual() returns false.
List<Employee> list1 = new List<Employee>()
{
new Employee { ID = 101, Name = "Mike"},
new Employee { ID = 102, Name = "Susy"},
};
List<Employee>
list2 = new List<Employee>()
{
new Employee { ID = 101, Name = "Mike"},
new Employee { ID = 102, Name = "Susy"},
};
var result = list1.SequenceEqual(list2);
Console.WriteLine("Are Equal = " + result);
To solve the problem in Example 6, there are 3 ways
1. Use the other overloaded version of SequenceEqual() method to which we can pass a custom class that implements IEqualityComparer
2. Override Equals() and GetHashCode() methods in Employee class
3. Project the properties into a new anonymous type, which overrides Equals() and GetHashCode() methods
We discussed implementing these 3 options for Distinct() method in previous article of LINQ Tutorial. In the same way these options can be implemented for SequenceEqual() method.
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