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I often need to perform LinQ queries to get distinct items from a IEnumerable based on one of its properties. I would like to know if this is a good way to wrap this operation:

<Extension()> Function DistinctOn(Of T)(iet As IEnumerable(Of T),
                                        identity_property As Func(Of T, Object)
                                       ) As IEnumerable(Of T)
    Return iet.GroupBy(identity_property).Select(Function(g) g.First)
End Function

Using example (pastas is a IEnumerable of Newtonsoft.Json.Linq.JObject):

Dim dpastas = pastas.DistinctOn(Function(jo) jo.Value(Of Integer)("id")).ToArray

It works Ok, but I'd like to know if it is good code also. Thank you very much!

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That is a good definition for an IQueryable but I believe it is better to implement the operation directly for an IEnumerable (note: I don't use VB, so translated from C#):

<Extension()> Public Iterator Function DistinctBy(Of T, TKey)(src As IEnumerable(Of T), keyFun As Func(Of T, TKey)) As IEnumerable(Of T)
    Dim seenKeys As New HashSet(Of TKey)()
    For Each e As T In src
        If seenKeys.Add(keyFun(e)) Then
            Yield e
        End If
    Next
End Function
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