Merge Two ArrayList in C#

Question

I want to merge all data in two arraylist in c#. Some data in arraylist got same with another arraylist. i don't want duplicate data when merge.

ArrayList1   ArrayList2
    1             1
    2             2
    3             4
                  5

I've try the coding below. but the result not as i expected:

for(int i = 0; i<arrayList2;i++)
{
  for(int j = 0; j<arrayList1;j++)
  {
     if(arraylist1[i] == arraylist2[j])
     {
        newArraylist.add(arraylist[i]+"-same");
     }
     else
     {
        newArraylist.add(arraylist[i]+"-from arrayList2");
     }
  }
}

The result from code above is :

newArrayList
   1 - same
   2 - same
   4 - from arraylist2
   5 - from arraylist2

the result that i want :

 newArrayList
       1 - same
       2 - same
       3 - from arraylist1
       4 - from arraylist2
       5 - from arraylist2

Given that you're using C# 2, is there any reason you're not using List<T>? — Jon Skeet
– Jon Skeet, Commented Jul 5, 2012 at 9:06
Erm, how can you expect an output of from arraylist1 when that's not even in your code snippet? — Shevek
– Shevek, Commented Jul 5, 2012 at 9:08
@JonSkeet i'm using the ArrayList because the old developer leave me this software with ArrayList.. owh why.-_-" — Qusyaire Ezwan
– Qusyaire Ezwan, Commented Jul 5, 2012 at 9:08

Wing · Accepted Answer · 2012-07-20 07:28:02Z

3

The most simple and easiest way is using LINQ

var collection1 = new ArrayList() { 1, 2, 3 };
var collection2 = new ArrayList() { 1, 2, 4, 5 };
var mergedList = new ArrayList();
mergedList.AddRange(collection1);
mergedList.AddRange(collection2.ToArray().Where(item => !collection1.ToArray().Contains(item)).ToList());
Console.WriteLine(String.Join(", ", mergedList.ToArray()));
Console.ReadLine();

answered Jul 20, 2012 at 7:28

Wing

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1 Comment

Andrew Stalker Over a year ago

collection1 doesn't need to be converted to an array to check Contains(item).

Filip Ekberg · Accepted Answer · 2012-07-05 09:17:16Z

2

How about this:

var arrayList1 = new ArrayList {1, 2, 3};
var arrayList2 = new ArrayList {1, 2, 4, 5};
var newList = new ArrayList();

foreach (var item in arrayList1)
{
    if(arrayList2.Contains(item))
    {
        newList.Add(string.Format("{0} - same", item));
        arrayList2.Remove(item);
    }
    else
    {
        newList.Add(string.Format("{0} - from arrayList1", item));
    }
}

foreach(var item in arrayList2)
{
    newList.Add(string.Format("{0} - from arrayList2", item));
}

This will give you this result:

1 - same
2 - same
3 - from arraylist1
4 - from arraylist2
5 - from arraylist2

answered Jul 5, 2012 at 9:17

Filip Ekberg

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Comments

nunespascal · Accepted Answer · 2012-07-05 09:14:46Z

1

Loop over the items and seee it it is contained in the first array.

foreach (int item in arrayList2)
{
    if (!arrayList1.Contains(item))
        arrayList1.Add(item);
}

answered Jul 5, 2012 at 9:14

nunespascal

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Comments

CodeCaster · Accepted Answer · 2012-07-05 09:08:39Z

0

You're comparing based on index, which won't work. ArrayList1[2] contains 3, while ArrayList1[2] contains 4.

You'll have to use .Contains() to check whether the number is present in the other list.

answered Jul 5, 2012 at 9:08

CodeCaster

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Comments

Trogvar · Accepted Answer · 2012-07-05 09:16:53Z

0

Code

var collection1 = new ArrayList() { 1, 2, 3 };
var collection2 = new ArrayList() { 1, 2, 4, 5 };

var merge = collection1.ToArray().Union(collection2.ToArray()).Distinct();
var result = new List<String>();
foreach (var val in merge)
{
    var newString = string.Empty;
    if (collection1.Contains(val) && collection2.Contains(val))
        newString = val.ToString() + " - same";
    else if (collection1.Contains(val))
        newString = val.ToString() + " - from list 1";
    else
         newString = val.ToString() + " - from list 2";
    Console.WriteLine(newString);
    result.Add(newString);
}

Produces output

1 - same
2 - same
3 - from list 1
4 - from list 2
5 - from list 2

answered Jul 5, 2012 at 9:16

Trogvar

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2 Comments

nunespascal Over a year ago

Union is a 3.5 feature. Not available in 2.0

Trogvar Over a year ago

My bad. Well, own Union() method can be written easily enough :)

juFo · Accepted Answer · 2012-07-20 07:36:10Z

0

The cleanest option would be using Union (LINQ). To find out how it works check this: http://www.dotnetperls.com/union

answered Jul 20, 2012 at 7:36

juFo

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