Compare two string array without using linq

Question

Possible Duplicate:
Comparing Arrays in C#

I have a two string arrays:

string[] a;
string[] b;

How can I identify how many (and what) items of a are not present in b? As I am using .NET 2.0 so I can't use linq.

Do you want to know the count or the items that are not present?What have you tried so far? — Priyank Patel, Aug 23 '12 at 15:59
@freebird I am reading one array in foreach and inside that foreach I am reading other array and then comparing each string one by one. — Zerotoinfinity, Aug 23 '12 at 16:01
http://stackoverflow.com/questions/713341/comparing-arrays-in-c-sharp — reggie, Aug 23 '12 at 16:05

Amiram Korach · Answer 1 · 2012-08-23T16:07:16.940

2

List<string> result = new List<string>();
foreach (string sa in a)
{
   if (Array.IndexOf(b, sa) < 0)
      result.Add(sa);
}

int count = result.Count;

edited Aug 23 '12 at 16:07

answered Aug 23 '12 at 16:02

Amiram Korach

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'System.Array' does not contain a definition for 'Contains' and no extension method 'Contains' accepting a first argument of type 'System.Array' could be found (are you missing a using directive or an assembly reference?) – Zerotoinfinity Aug 23 '12 at 16:03
I believe that requires LINQ too – Zerotoinfinity Aug 23 '12 at 16:04
1

Edited my answer. It's really hard to remember what was in 2.0. I had to avoid "var" 3 times! – Amiram Korach Aug 23 '12 at 16:07

score 1 · Answer 2 · answered Aug 23 '12 at 16:05

1

convert them both to a List the do something like this:

List<string> difference = new List<string>();
foreach(string word in a)
{
    if(!b.Contains(word))
        difference.Add(word);
}

answered Aug 23 '12 at 16:05

Nicolas Brown

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score 1 · Answer 3 · edited May 23 '17 at 12:04

1

I would recommand to transform your arrays of strings into HashSet<T>s.
See here for how to use a HashSet<T> in .NET 2.0

Then

How can I identify how many (and what) items of a are not present in b?

--> IntersectWith does precisely that.

edited May 23 '17 at 12:04

Community

1
1

answered Aug 23 '12 at 16:08

Louis Kottmann

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IntersectWith is only .Net 3.5+ – Joshua Honig Aug 23 '12 at 16:09
@jmh_gr .Net 3.5 and .Net 2.0 share the same DLR, see the first link for more information. – Louis Kottmann Aug 23 '12 at 16:10

score 1 · Answer 4 · answered Aug 23 '12 at 16:10

1

Try this:

string[] a = ...;
string[] b = ...;

List<string> bList = new List<string>(b);
List<string> valuesInAButNotInB = new List<string>();
foreach (string value in a)
{
    if (!bList.Contains(value))
        valuesInAButNotInB.Add(value);
}

answered Aug 23 '12 at 16:10

Dan

9,717
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score 1 · Answer 5 · answered Aug 23 '12 at 16:14

What you need to do is store the items from one list in a set, and then remove all of the items from that set if they are in the other collection. This will be much quicker for larger data sets than two nested loops, or performing lots of linear searches on one of the arrays.

Since HashSet doesn't exist in 2.0 I just use a Dictionary and ignore the values. It's a hack, but not a terrible one at that.

string[] a = null;
string[] b = null;
Dictionary<string, string> values = new Dictionary<string, string>();
foreach (string s in a)
{
    values.Add(s, s);
}

foreach (string s in b)
{
    values.Remove(s);
}

foreach (string s in values.Keys)
{
    Console.WriteLine(s);//This string is in 'a' and not in 'b'
}

ken2k · Accepted Answer · 2012-08-23T16:11:46.950

Just enumerate items in both a and b, just like in the old days:

private static void Main(string[] args)
{
    string[] a = new string[] { "a", "b", "c", "d" };
    string[] b = new string[] { "c", "d" };

    foreach (string tmp in a)
    {
        bool existsInB = false;
        foreach (string tmp2 in b)
        {
            if (tmp == tmp2)
            {
                existsInB = true;
                break;
            }
        }

        if (!existsInB)
        {
            Console.WriteLine(string.Format("{0} is not in b", tmp));
        }
    }

    Console.ReadLine();
}

MethodMan · Answer 7 · 2012-08-23T16:41:36.290

-1

private List<string> CompareArray(string[]  arr1, string[] arr2)
{
        List<string> compareList = new List<string>();
        //iterate throught it
        foreach( string str in arr1 )
        {
            if(!arr2.Contains( str ))
            {
                compareList.Add(str);
            }
        }
            return compareList;
 }

edited Aug 23 '12 at 16:41

answered Aug 23 '12 at 16:03

MethodMan

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http://stackoverflow.com/questions/713341/comparing-arrays-in-c-sharp – reggie Aug 23 '12 at 16:04
1

This isn't what he wants. He wants the set difference, not sequence equality. The two are quite different. – Servy Aug 23 '12 at 16:15
@DJKRAZE You've changed it to now be set equality, rather than sequence equality (it doesn't require the same ordering) but it's still not a set difference. It needs to return the set of items in `a` that are not in `b`. That won't be a boolean value. The return type of your method alone tells you this isn't right. – Servy Aug 23 '12 at 16:38
I thought I edited the answer .. sorry about that I just updated I will review again as well – MethodMan Aug 23 '12 at 16:42

Compare two string array without using linq

7 Answers7