Regex to Match Json array element in C#

Question

I need to match element of the JSON array element in c# for filter autocomplete in c#. Here is my code:

string firstname = "h";
List<user> userlist = new List<user>();
user user1 = new user();
user1.firstname = "Hardik";
user1.lastname = "Gondalia";
userlist.Add(user1);

user user2 = new user();
user2.firstname = "John";
user2.lastname = "Abraham";
userlist.Add(user2);

user user3 = new user();
user3.firstname = "Will";
user3.lastname = "Smith";
userlist.Add(user3);

user user4 = new user();
user4.firstname = "Martin";
user4.lastname = "Luthor";
userlist.Add(user4);

var myRegex = new Regex(".*\\b" + firstname + "\\b.*");
var u = userlist.Where(i => myRegex.IsMatch(i.firstname)).ToList();
return Json(u, JsonRequestBehavior.AllowGet);

When I pass character "h" as firstname, I am getting count of u = 0; I am expecting user1 and user2 in variable u.

"I am expecting user1 and user2" - why? \bh\b will only match the lone standing h because of the "word boundary" \b... Perhaps start by reading a regex tutorial. — CodeCaster
– CodeCaster, Commented Aug 3, 2016 at 10:11
Well, these first names do not contain h as a whole word. And Hardik contains an uppercase H (pass RegexOptions.IgnoreCase flag to myRegex). Also, Regex.IsMatch also finds partial matches, you do not need .* in your pattern at all. Judging by the code, you may achieve that without a regex, use userlist.Where(i => culture.CompareInfo.IndexOf(i.firstname, firstname, CompareOptions.IgnoreCase) >= 0).ToList() (see stackoverflow.com/questions/444798/…) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 3, 2016 at 10:12
@CodeCaster : you mean to say that \b will match whole word rather then individual character? — Hardik Gondalia
– Hardik Gondalia, Commented Aug 3, 2016 at 10:14
@zerkms : I thought regex was good alternative. Any other approach is most welcome. — Hardik Gondalia
– Hardik Gondalia, Commented Aug 3, 2016 at 10:18

Wiktor Stribiżew · Accepted Answer · 2017-09-25 07:11:04Z

1

I am posting an answer since there are several issues here.

First, these first names do not contain h as a whole word and you defined \b in your pattern to match a first name as a whole word.

Second, Hardik contains an uppercase H (so, you should consider passing RegexOptions.IgnoreCase flag to myRegex).

Third, Regex.IsMatch also finds partial matches, you do not need .* in your pattern at all.

Judging by the code, you may achieve that without a regex, use

userlist.Where(i => culture.CompareInfo.IndexOf(i.firstname, firstname, CompareOptions.IgnoreCase) >= 0).ToList()

edited Sep 25, 2017 at 7:11

answered Aug 3, 2016 at 11:03

Wiktor Stribiżew

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