Unique array of vb.net structures
I have a structure
Public Structure MyRecords
Dim record_name As String
Dim record_surname As String
End Structure
and an array of structures
Dim Records_arr(100000) AS MyRecords
The array is filled with data, but I want to remove the duplicate MyRecords
.
Duplicate means:
Records_arr(3).record_name = "John"
Records_arr(3).record_surname = "Doe"
Records_arr(99).record_name = "John"
Records_arr(99).record_surname = "Doe"
In this example, I want to delete Records_arr(3)
or Records_arr(99)
or just delete the values of one of them.
I have already implemented a two-pass top-down and then bottom-up scan that wipes out duplicates, but very slowly. There must be a better way?
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Inject IEquatable<T>
into your structure and then use the LINQ function Distinct()
to get your goals.
Here's an example implementation:
Public Structure MyRecords
Implements IEquatable(Of MyRecords)
Dim record_name As String
Dim record_surname As String
Public Function Equals1(other As MyRecords) As Boolean Implements IEquatable(Of MyRecords).Equals
Return record_name.Equals(other.record_name) AndAlso record_surname.Equals(other.record_surname)
End Function
End Structure
Now you can call Records_arr.Distinct()
and it will return unique entries of your array.
Further explanation
In response to your comment, here's what's going on. Since you're using Structure
, not Class
, MyRecords
already inherits the method ValueType.Equals()
. For value types that do not contain reference type members, the method Equals()
performs a byte comparison of two objects in memory. On the other hand, if it contains elements of a reference type (this is your case), it uses Reflection to compare the corresponding fields of the two instances. You have two fields String
in your structure that are reference types and are therefore compared via Reflection. (It's important to note that the class String
, although a reference type, overrides Equals()
to provide value comparison instead of standard reference comparison). This way, even if you don't implement IEquatable
or IComparable
in your class,Distinct()
will work fine using the default function ValueType.Equals()
.
Note, however, that MSDN asks you to provide an implementation Equals()
for such structures. Here's a relevant passage:
In particular, if your value type contains fields that are reference types, you must override the Equals (Object) method. This can improve performance and give you a more accurate idea of the value of equality for a type.
Read more about this in this MSDN article .
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