How do I remove emoji characters from a string?

Question

I've got a text input from a mobile device. It contains emoji. In C#, I have the text as

Text  text

Simply put, I want the output text to be

Text text

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I'm trying to just remove all such emojis from the text with rejex.. except, I'm not sure how to convert that emoji into it's unicode sequence.. How do I do that?

edit:

I'm trying to save the user input into mysql. It looks like mysql UTF8 doesn't really support unicode characters and the right way to do it would be by changing the schema but I don't think that is an option for me. So I'm trying to just remove all the emoji characters before saving it in the database.

This is my schema for the relevant column:

I'm using Nhibernate as my ORM and the insert query generated looks like this:

Insert into `Content` (ContentTypeId, Comments, DateCreated) 
values (?p0, ?p1, ?p2);
?p0 = 4 [Type: Int32 (0)]. ?p1 = 'Text  text' [Type: String (20)], ?p2 = 19/01/2015 10:38:23 [Type: DateTime (0)]

When I copy this query from logs and run it on mysql directly, I get this error:

1 warning(s): 1366 Incorrect string value: '\xF0\x9F\x98\x80 t...' for column 'Comments' at row 1   0.000 sec

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Also, I've tried to convert it into encoding bytes and it doesn't really work..

Answer 1

Assuming you just want to remove all non-BMP characters, i.e. anything with a Unicode code point of U+10000 and higher, you can use a regex to remove any UTF-16 surrogate code units from the string. For example:

using System;
using System.Text.RegularExpressions;

class Test
{
    static void Main(string[] args)
    {
        string text = "x\U0001F310y";
        Console.WriteLine(text.Length); // 4
        string result = Regex.Replace(text, @"\p{Cs}", "");
        Console.WriteLine(result); // 2
    }
}

Here "Cs" is the Unicode category for "surrogate".

It appears that Regex works based on UTF-16 code units rather than Unicode code points, otherwise you'd need a different approach.

Note that there are non-BMP characters other than emoji, but I suspect you'll find they'll have the same problem when you try to store them.

Additionally, not that this won't remove emojis in the BMP, such as U+2764 (red heart). You can use the above as an example of how to remove characters in specific Unicode categories - the category for U+2764 is "other symbol" for example. Now whether you want to remove all "other symbols" is a different matter.

But if really you're interested in just removing surrogate pairs because they can't be stored properly, the above should be fine.