How to retrieve the most frequent element from an array list

Since you're getting it from a database anyway, let it do the work. It's good at this kind of thing. The query is something like this (may not quite be right, I'm not a database guy):

query = "select free_dates, count(free_dates) as number from I_mgr_free_dates where vacancy_id=" + "\'" + DropDownList1.SelectedItem + "\'" group by free_dates order by count desc limit 1";

Remember that if that dropdown list contains information entered by the user, pulled from an external configuration file etc you need to escape it to avoid SQL injection attacks. Use a parameterised query if possible.

Frequency as in the number of times a specific item appears or did you mean closest date to the current date?

If its the first then you'll have to setup a counter and increment each date that is matched or insert it into your match array/list. If its the second then you'll have to compare dates.

Hi,

You can use List of KeyValuePair (contains Keyword and count of it as pair) to count each element you read
to the most frequent element from it.

good luck

I am not sure by what you mean as "the most frequent" but either way you can use LINQ.

(Side note.. You could use List[DateTime] instead of ArrayList... no casting then. I will use this for simplicity)

Assume you mean the most recent...

List<datetime> list = new List<datetime>
...

var now = DateTime.Now;
var mostRecent = list.Min(date => now - date);

</datetime></datetime>

If you mean the "most common" then you can use LINQ to find the highest count.

DateTime highCountValue = null;
int count = int.MinValue;
list.ForEach(dateTime =>
{
    var potentialCount = list.Count(d => d == dateTime);
    if(potentialCount > count)
    {
        count = potentialCount;
        highCountValue = dateTime;
    }
});

int count = 1;
                int currentIndex = 0;
                int i;
                for (i = 1; i < list.Count; i++)
                {
                    if (list[i] == list[currentIndex])
                        count++;
                    else
                        count--;
                    if (count == 0)
                    {
                        currentIndex = i;
                        count = 1;
                    }

                }

                DateTime day2 = (DateTime)list[currentIndex];
                MessageBox.Show(day2.ToString());

i used this code.but this gives last element of the array.

assume there is an array,
{1,3,4,1,3,1}
the most frequent element is 1.
i wanna get that out put.