C# the best way to compare 4 strings and ignore the empty one

Question

I want to compare 4 strings if they are equal or not. The problem is that I have to ignore the empty strings, but if they are all empty then the method must also return true, because all empty strings are equal. I could write everything down like

if(string1 != string.Empty && string2 != string.Empty &&
               string1 != string2)
{
   return false
}
if(string1 != string.Empty && string2 != string.Empty &&  string3 != etc....

But I think there is a better way then writing out all the possibilities. But how?

Compare 4 strings: how? To order them, or to see if they are equal? — Richard, Mar 23 '16 at 09:03
Can you please expand a but on what you are attempting to do? — Jamie Rees, Mar 23 '16 at 09:03
So do all four have to be equal or do they have to be pairwise equal? Furthermore can at least one item be empty or non at all? — MakePeaceGreatAgain, Mar 23 '16 at 09:04
@Kimos you definitely need to put them into array, then this answer will help you http://stackoverflow.com/questions/5307172/check-if-all-items-are-the-same-in-a-list. — Sergiy Kozachenko, Mar 23 '16 at 09:10
the strings should all be equal. but if they are all empty then the methode must also return true, because all empty strings are equal — Kimos, Mar 23 '16 at 09:28

Matthew Watson · Accepted Answer · 2016-03-23T10:07:54.583

This will check that all non-empty or non-null strings are equal:

public static bool CheckNonEmptyStringsForEquality(params string[] strings)
{
    string target = strings.FirstOrDefault(s => !string.IsNullOrEmpty(s));

    if (target == null)
        return false;

    return strings.All(s => string.IsNullOrEmpty(s) || s == target);
}

Use it like this:

Console.WriteLine(
    CheckNonEmptyStringsForEquality("", "X", "X")); // Prints true

Console.WriteLine(
    CheckNonEmptyStringsForEquality("", "X", "Y")); // Prints false

Console.WriteLine(
    CheckNonEmptyStringsForEquality("", "X", "", "X", "", "X", "")); // Prints true

Note: If you want to return true if all strings are null or empty, do this instead:

public static bool CheckNonEmptyStringsForEquality(params string[] strings)
{
    string target = strings.FirstOrDefault(s => !string.IsNullOrEmpty(s));
    return strings.All(s => string.IsNullOrEmpty(s) || s == target);
}

Then this will return true too:

Console.WriteLine(
CheckNonEmptyStringsForEquality("", "", "")); // Prints true

didnt work, i am getting false when the array contain one empty string and others strings are equal — Kimos, Mar 23 '16 at 09:29
@Kimos Post the code that doesn't work and I should be able to explain what you did wrong. If you look at the very first usage example I gave above, you can see that it returns true when the array contains one empty string and the other strings are equal. The code I posted definitely works. — Matthew Watson, Mar 23 '16 at 10:04

score 2 · Answer 2 · answered Mar 23 '16 at 09:07

2

Something like this? Do Distinct and check the Count on an Array of strings.

var strings = new string[] {"str1", "str2", "str3"};

if( (strings.Where(s=>!string.IsNullOrEmpty(s)).Distinct().Count() == 1))
{       
    // unique
}

answered Mar 23 '16 at 09:07

Hari Prasad

16,716
4
21
35

1

The question is not clear but i understand from the example that we search if "any 2 strings" are equals, not if "all" are equals (meaning `strings.Distinct().Count() < strings.Count()`) – tafia Mar 23 '16 at 09:11
Query is correct, `count` will be 1 if we have same string across. – Hari Prasad Mar 23 '16 at 09:12
so I guess I didn't understand the question – tafia Mar 23 '16 at 09:18

score 1 · Answer 3 · answered Mar 23 '16 at 09:18

1

Try this:

    static void Main(string[] args)
    {
        var text1 = new[] { "x", "y", "z", "w" };
        var text2 = new[] { "x", "y", null, "" };
        var text3 = new[] { "x", "x", "x", "x" };
        var text4 = new[] { "x", "x", null, "" };

        MyComparer(text1); // False
        MyComparer(text2); // False
        MyComparer(text3); // True
        MyComparer(text4); // True
    }

    private static bool MyComparer(IEnumerable<string> array)
    {
        return array.Where(t => !string.IsNullOrEmpty(t)).Distinct().Count() == 1;
    }

answered Mar 23 '16 at 09:18

cani

91
7

var text5 = new[] { "", "", "", "" }; returns false, should be true all empty strings are euqal... – Kimos Mar 23 '16 at 09:58
I do not think the question states that it should return true or false. If so, it should be described as such. – cani Mar 23 '16 at 11:07

Venu prasad H S · Answer 4 · 2016-03-23T12:44:56.607

0

if you pass the string in an array,

var collection = new string[] { "India", "", "India", "India" };
var isEqual = collection.Distinct().Contains("") ? collection.Distinct().Count() <= 2 : collection.Distinct().Count() == 1;

edited Mar 23 '16 at 12:44

answered Mar 23 '16 at 09:16

Venu prasad H S

231
1
8

this will result in false if all strings are empty, which is not correct – Kimos Mar 23 '16 at 09:27
Thanks @Kimos. Now the code returns true even if all the strings are empty – Venu prasad H S Mar 23 '16 at 12:46

score 0 · Answer 5 · answered Mar 23 '16 at 09:33

        //Hope this helps
        string a = "";
        string b = "mystring";
        string c = "mystring";
        string d = "mystring";
        bool isEqual = true;
        ArrayList array = new ArrayList();
        array.Add(a);
        array.Add(b);
        array.Add(c);
        array.Add(d);


        foreach (string stringMemeber in array)
        {
            if (string.IsNullOrEmpty(stringMemeber))
            {
                continue;
            }
            else
            {
                foreach (string NestedStringMember in array)
                {
                    if (string.IsNullOrEmpty(NestedStringMember))
                    {
                        continue;
                    }
                    else
                    {
                        if (string.Compare(stringMemeber,NestedStringMember)!=0)
                        {
                            isEqual = false;
                            break;
                        }
                    }
                }

                if (!isEqual)
                {
                    break;
                }

            }
        }


        Console.WriteLine("The strings are equal: " + isEqual.ToString());

You can check equality of every member in an array using a single loop. There's no need for the second `foreach`: it's just doing extra work. — RoadieRich, Mar 23 '16 at 17:17

C# the best way to compare 4 strings and ignore the empty one

5 Answers5