CODEWITHSUNDEEP
c#regex
Json
Json

Reputation: 35

Regular expression to find 3 repeated words

I'm trying to create a regular expression which matches the same word 3 times, they are separated by a comma. For example, some inputs would be:

HEY,HEY,HEY - match
NO,NO,NO - match
HEY,HI,HEY - no match
HEY,H,Y - no match
HEY,NO,HEY - no match

How can I go about doing this? I've had a look at some example but they are only good for characters, not words.

Upvotes: 2

Views: 1320

Answers (1)

vyrp
vyrp

Reputation: 939

This should do the trick:

^(\w+),\1,\1$

Explanation:

^: beginning of the line. Needed to avoid matching "HHEY,HEY,HEY".

(\w+): matches one or more word characters. This is the first catpured group.

,: the character comma.

\1: a backreference to the first captured group. In the other words, matches whatever was matched in (\w+) before.

,: the character comma.

\1: a backreference to the first captured group.

$: end of the line. Needed to avoid matching "HEY,HEY,HEYY".

Source: https://msdn.microsoft.com/en-us/library/az24scfc(v=vs.110).aspx#Anchor_5

Example usage

static void Main()
{
    var threeWords = new Regex(@"^(\w+),\1,\1$");
    var lines = new[]
    {
        "HEY,HEY,HEY",
        "NO,NO,NO",
        "HEY,HI,HEY",
        "HEY,H,Y",
        "HEY,NO,HEY",
        "HHEY,HEY,HEY",
        "HEY,HEY,HEYY",
    };

    foreach (var line in lines)
    {
        var isMatch = threeWords.IsMatch(line) ? "" : "no ";
        Console.WriteLine($"{line} - {isMatch}match");
    }
}

Output:

HEY,HEY,HEY - match
NO,NO,NO - match
HEY,HI,HEY - no match
HEY,H,Y - no match
HEY,NO,HEY - no match
HHEY,HEY,HEY - no match
HEY,HEY,HEYY - no match

Upvotes: 8

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