Regex.Matches return no duplicates?

Question

Hello

Dim blah As MatchCollection = Regex.Matches(text, "([a-zA-Z0-9_-.]+)@([a-zA-Z0-9_-.]+).([a-zA-Z]{2,9})", RegexOptions.CultureInvariant Or RegexOptions.IgnoreCase Or RegexOptions.Multiline)

How may I force Regex.Matches not to return duplicate items, so MatchCollection will not contain duplicates (case insensitive)?

If not possible, remove duplicates from MatchCollection?

Efficiency and speed is crucial :(

Thanks :)

Answer 1

If you are interested in a regular expression that excludes duplicates, try this: (?<m>([a-zA-Z0-9_\-\.]+)@([a-zA-Z0-9_\-\.]+)\.([a-zA-Z]{2,9}))(?!.*\<m>).

It can be compared with DistinctBy:

Dim matches = Regex.Matches(Text, "your original expression...", RegexOptions.CultureInvariant Or RegexOptions.IgnoreCase Or RegexOptions.Multiline).DistinctBy(Function(m) m.Value, StringComparer.CurrentCultureIgnoreCase)

The experiments with typical data will show the fastest method.

Answer 2

Try the following

Dim matches As MatchCollection = Regex.Matches(text, "([a-zA-Z0-9_-.]+)@([a-zA-Z0-9_-.]+)\.([a-zA-Z]{2,9})", RegexOptions.CultureInvariant Or RegexOptions.IgnoreCase Or RegexOptions.Multiline)
Dim uniqueMatches As New HashSet(Of String)(StringComparer.OrdinalIgnoreCase)
For Each match As Match In matches
    If match.Success Then
        uniqueMatches.Add(match.Value)
    End If
Next
' Now uniqueMatches contains only unique email addresses, case-insensitively

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hth

Marcin