Method to get the count of an element in an array within specified range

Question

If I have an ArrayList called holder: {2,3,3,5,4,7,1,7,8,4}. Let say I wanted to find the count of certain element's occurrence in the above array within a certain range, I have these function:

In VB.Net:

Private Function getValInRange(ByVal lowerVal As Integer, ByVal upperVal As Integer, ByVal holder As ArrayList) As Integer
        Dim count As Integer = 0
        For Each item As Integer In holder
            If (item <= upperVal AndAlso item >= lowerVal) Then
                count = count + 1
            End If
        Next
        Return count
End Function

In C#:

private int getValInRange(int lowerVal, int upperVal, ArrayList holder)
{
    int count = 0;
    foreach (int item in holder)
    {
        if ((item <= upperVal && item >= lowerVal))
        {
            count = count + 1;
        }
    }

    return count;
}

So, when I query count = getValInRange(3,5,holder), I shall get a return of 5

I know the above function will be able to satisfy my needs, but I wonder if there is already a built in function that I can use. I plan to clean up my code and learn at the same time. Thanks a lot...

Do you have to use the non-generic ArrayList? That's been somewhat-obsolete since 2005. If you could use some implementation of IEnumerable<int> (e.g. List<int> or int[]) it would be much simpler. I'd also suggest following .NET naming conventions - I'd call the method CountValuesInRange for example. — Jon Skeet
– Jon Skeet, Commented Jan 25, 2018 at 7:38
@Jon Skeet I am using ArrayList all the time. But you suggestion to use different implementation is good. Maybe shall start to use that from my next attempt onwards. Anyway, I prefer to not to have a separate method CountValuesInRange — Hari
– Hari, Commented Jan 25, 2018 at 7:54
"I am using ArrayList all the time" - I'd stop doing that if I were you. I wouldn't wait, I'd learn about generic collections right now. — Jon Skeet
– Jon Skeet, Commented Jan 25, 2018 at 7:55
@JonSkeet thanks for your suggestion man. I learned something new — Hari
– Hari, Commented Jan 25, 2018 at 7:56

Sweeper · Accepted Answer · 2018-01-25 07:51:39Z

4

I don't think there is such a built-in method in .NET Core, but you can write this more concisely, using Enumerable.Where.

 holder.Cast<int>().Where(x => x <= upperLimit && x >= lowerLimit).Count()

ArrayList is actually obsolete. If you don't have to stick with it, try changing to a List<int>. That way, you don't need the call to Cast:

 holder.Where(x => x <= upperLimit && x >= lowerLimit).Count()

Alternatively,

 holder.Count(x => x <= upperLimit && x >= lowerLimit)

The x => ... thing, if you didn't know, is called a lambda expression, learn more about them here.

There are lots of other cool methods that help you with dealing with IEnumerable<T> in the System.Linq namespace! This cool collection of helper methods is called Language INtegrated Query (LINQ).

edited Jan 25, 2018 at 7:51

answered Jan 25, 2018 at 7:45

Sweeper

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2 Comments

Aleks Andreev Over a year ago

You can write it shorter if you put lambda inside Count and remove Where

Andrew Morton Over a year ago

OP also asked for VB, so holder.Sum(Function(x) If(x >= lowerVal AndAlso x <= upperVal, 1, 0)) as .Count in VB 15.0 (2017) doesn't accept a lambda. Or just the .Where....Count version.

Guy · Accepted Answer · 2018-01-25 08:04:35Z

4

If you use List<int>, or any other IEnumerable<int>, Linq has the Count extension

private int getValInRange(int lowerVal, int upperVal, List<int> holder)
{
    return holder.Count(item => item <= upperVal && item >= lowerVal);
}

Edit: As @MarcGravell suggested, you can also cast the ArrayList to IEnumerable

private int getValInRange(int lowerVal, int upperVal, ArrayList holder)
{
    return holder.Cast<int>().Count(item => item <= upperVal && item >= lowerVal);
}

edited Jan 25, 2018 at 8:04

answered Jan 25, 2018 at 7:44

Guy

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1 Comment

Marc Gravell Over a year ago

Note you can still use this with ArrayList, but you'd need to use .Cast<int>().Count(...) - although I agree that moving away from ArrayList is hugely desirable

Mohammad Karimi · Accepted Answer · 2018-01-25 07:49:47Z

1

I would suggest to use LINQ and change that ArrayList to IEnumerable, however using IEnumerable<int> is more preferred.

private int GetValInRange(int lowerVal, int upperVal, IEnumerable holder)
    {
        return holder.Cast<int>().Count(item => item <= upperVal && item >= lowerVal);
    }

answered Jan 25, 2018 at 7:49

Mohammad Karimi

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1 Comment

Hari Over a year ago

Unfortunately using ArrayList currently

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