Replacing a number which comes after a tab with regex code

Question

I am working on a question bank generator using vb.net. Each question has 4 options which starts with a tab and 1),2)3),4)

I am using [^\(|\d][1-4]\), "#" which replaces 1),2),3),4)(option numbers) with #

But it also replaces 1), 2), 3),4) when ever it comes in the Question and Options with #.

Example

17.  Specific heat of certain element is 0.064, its approximate atomic mass is
    1) 100 U    2) 10 U 3) 20 U 4)  Both  2) and 3)

Output is

17. Specific heat of certain element is 0.064, its approximate atomic mass is
    # 100 U # 10 U  # 20 U  #  Both # and #

Expected

 17. Specific heat of certain element is 0.064, its approximate atomic mass is
    # 100 U # 10 U  # 20 U  #  Both 2) and 3)

Maybe you should separate the model from the view. You could store the questionnaire as XML instead of plain text. E.g. an option would be represented in a structured way as `` and it would be displayed as `1) 100 U`. This makes it a lot easier to read the attributes by using the classes form the [System.Xml.Linq Namespace](https://learn.microsoft.com/en-us/dotnet/api/system.xml.linq?view=net-5.0). — Olivier Jacot-Descombes, Jan 16 '21 at 16:39
Also see my answer to [Questionnaire database design - which way is better?](https://dba.stackexchange.com/a/11970/6257). — Olivier Jacot-Descombes, Jan 16 '21 at 16:47

The fourth bird · Answer 1 · 2021-01-16T17:36:00.273

1

One option is to use a positive lookbehind to assert a tab directly to the left, then match a digit 1-4 followed by a )

In the replacement use a #

(?<=\t)[1-4]\)

(?<=\t) Positive lookbehind, match a tab directly to the left
[1-4] Match a digit 1 to 4
\) Match a ) char

.NET Regex demo | Vb.net demo

Dim input As String = "17.   Specific heat of certain element is 0.064, its approximate atomic mass is" & vbCrLf &
"1) 100 U   2) 10 U 3) 20 U 4)  Both  2) and 3)"
Dim regex As Regex = New Regex("(?<=\t)[1-4]\)")
Dim result As String = regex.Replace(input, "#")

Output

17.  Specific heat of certain element is 0.064, its approximate atomic mass is
1) 100 U    # 10 U  # 20 U  #  Both  2) and 3)

Console.WriteLine(result) Console.WriteLine(result)

Another option is to match a tab, 1+ digits and the ). In the replacement user a tab and #

\t\d+\)

Vb.net demo

edited Jan 16 '21 at 17:36

answered Jan 16 '21 at 16:51

The fourth bird

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Thank you , but "\t " is not working in vb.net code – Raja Gopal Jan 16 '21 at 17:22
@RajaGopal See https://stackoverflow.com/questions/1410462/vb-net-identifier-for-tab or https://stackoverflow.com/questions/30755944/regex-vb-net-regex-replace – The fourth bird Jan 16 '21 at 17:23
@RajaGopal I have added a code demo for both patterns – The fourth bird Jan 16 '21 at 17:36
Here `\t` is interpreted as tabulator in the regular expression. It must not be interpreted as tabulator in VB (were indeed it isn't as it would in C# if not inside a verbatim string). – Olivier Jacot-Descombes Jan 16 '21 at 18:14
@OlivierJacot-Descombes In the second code example I have used `ControlChars.Tab` to be used in the replacement. – The fourth bird Jan 16 '21 at 18:19

Replacing a number which comes after a tab with regex code

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