列表中的最大值和最小值

Question

I'm currently doing my current project and I had a problem. Here's what the project needs to do:

Find the maximum and the minimum temperature from a certain range of date. The range of the date will be inputted by the user.

So, I make a form as the main menu for inputting the items and finding the maximum and minimum value (both in the new form). I also make a class to store the items:

public class TempDate
{
    public double Temp { get; set; }

    public DateTime Date { get; set; }
}

In the first form, just call it FormAddData , from here items will be stored into the list using a textbox and here's the code:

private void buttonSubmit_Click(object sender, EventArgs e)
    {
        FormMenu formMenu = (FormMenu)this.Owner;

        DateTime date = dateTimePickerDate.Value.Date;
        double temp = double.Parse(textBoxTemp.Text);

        TempDate tempDate = new TempDate();

        tempDate.Date = date;
        tempDate.Temp = temp;

        formMenu.listOfTempDate.Add(tempDate);
        listBoxInfo.Items.Add(date + "\t" + temp + "°C");
    }

In the second form that called FormMaxMinRange . In this form, I use two DateTimePicker the first one for the starting date and the second for the ending date. From here I need to make a button that will select all the items from the range that I used from starting and ending date. Here's my code:

private void buttonMaxMin_Click(object sender, EventArgs e)
    {
        FormMenu formMenu = (FormMenu)this.Owner;

        DateTime start = dateTimePickerStart.Value.Date;
        DateTime end = dateTimePickerEnd.Value.Date;
        int highest = 0;
        double max = formMenu.listOfTempDate[0].Temp;
        int lowest = 0;
        double min = formMenu.listOfTempDate[0].Temp;

        for (int i = 1; i < formMenu.listOfTempDate.Count; i++)
        {
            if (formMenu.listOfTempDate[i].Date >= start
                && formMenu.listOfTempDate[i].Date <= end)
            {
                if (formMenu.listOfTempDate[i].Temp > max)
                {
                    highest = i;
                    max = formMenu.listOfTempDate[i].Temp;
                }

                if (formMenu.listOfTempDate[i].Temp < min)
                {
                    lowest = i;
                    min = formMenu.listOfTempDate[i].Temp;
                }
            }
        }
        listBoxMaxMin.Items.Add("");
        listBoxMaxMin.Items.Add("Lowest temp: " + min + ", on " + formMenu.listOfTempDate[lowest].Date);
        listBoxMaxMin.Items.Add("Highest temp: " + max + ", on " + formMenu.listOfTempDate[highest].Date);
    }

Here's the main form that i declared the class (which include the list):

public partial class FormMenu : Form
{
    public List<TempDate> listOfTempDate = new List<TempDate>();

    public FormMenu()
    {
        InitializeComponent();
    }

    private void fromCertainRangeToolStripMenuItem_Click(object sender, EventArgs e)
    {
        FormMaxMinRange formMaxMinRange = new FormMaxMinRange();
        formMaxMinRange.Owner = this;
        formMaxMinRange.ShowDialog();
    }
}

But, the problem is, the minimum value was not selected inside the range of selection. Also I want the max and min value was printed in the listbox. Sorry for the long and weird question. I hope someone can understand what I means with this question to complete my project. Thank you.

Answer 1

See this code snippet. You can use Linq to select the reduced list (with Start/Enddate) and order it by Temp. Now you can easy select the first (min) and the last (max) object.

List<TempDate> loTempDateList = new List<TempDate>()
{
    new TempDate() {Date = DateTime.Now.AddDays(-10), Temp = 10.01 },
    new TempDate() {Date = DateTime.Now.AddDays(-5), Temp = 20.01 },
    new TempDate() {Date = DateTime.Now.AddDays(-3), Temp = 30.01 },
    new TempDate() {Date = DateTime.Now, Temp = 40.01 }
};
DateTime ldStart = DateTime.Now.AddDays(-6);
DateTime ldEnd = DateTime.Now.AddDays(-1);

var loDateList = loTempDateList.Where(item => item.Date <= ldEnd && item.Date >= ldStart)
    .OrderBy(item => item.Temp);

TempDate loMin = loDateList.First();
TempDate loMax = loDateList.Last();

Console.WriteLine("{0}: {1} with max temp", loMax.Date, loMax.Temp);
Console.WriteLine("{0}: {1} with min temp", loMin.Date, loMin.Temp);

Output (for today):

9/26/2017 3:17:09 PM: 30.01 with max temp
9/24/2017 3:17:09 PM: 20.01 with min temp

Update (with your variable names):

Copy this under DateTime end = dateTimePickerEnd.Value.Date; in your Form

var loDateList = listOfTempDate.Where(item => item.Date <= end && item.Date >= start)
    .OrderBy(item => item.Temp);

TempDate loMin = loDateList.FirstOrDefault();
TempDate loMax = loDateList.LastOrDefault();

if (loMin != null && loMax !=  null)
{
    listBoxMaxMin.Items.Add("");
    listBoxMaxMin.Items.Add("Lowest temp: " + loMin.Temp + ", on " + loMin.Date);
    listBoxMaxMin.Items.Add("Highest temp: " + loMax.Temp + ", on " + loMax.Date);
}

Answer 2

I would suggest you use Linq Max and Min methods.

// filter out only the dates in the range you need
var items = formMenu.listOfTempDateWhere(
    item => ((TempDate)item).Date >= start && ((TempDate)item).Date <= end
);

// get the maximum value
var max = items.Max(item => item.Temp);
// get the minimum value
var min = items.Min(item => item.Temp);

Just remember to add using System.Linq on the top of your .cs file

---

try this online

Answer 3

If you don't like a LINQ approach (I never use LINQ, for some, possibly invalid reason, I think it's evil), you can override the List class and extend it with methods of your own.

public class TempDataList<T> : List<TempData>
{
    public TempDataList() : base()
    {
    }

    public TempDataList(IEnumerable<TempData> collection) : base(collection)
    {
    }

    public TempData GetMaxTemp(DateTime startDate, DateTime endDate)
    {
        TempData highestTempData = null;
        for (int i = 0; i < this.Count; i++)
        {
            if (this[i].Date >= startDate && this[i].Date <= endDate)
            {
                if (highestTempData == null || this[i].Temp > highestTempData.Temp)
                {
                    highestTempData = this[i];
                } 
            }
        }
        return highestTempData;
    }

    public TempData GetMinTemp(DateTime startDate, DateTime endDate)
    {
        TempData lowestTempData = null;
        for (int i = 0; i < this.Count; i++)
        {
            if (this[i].Date >= startDate && this[i].Date <= endDate)
            {
                if (lowestTempData == null || this[i].Temp < lowestTempData.Temp)
                {
                    lowestTempData = this[i];
                }
            }
        }
        return lowestTempData;
    }
}

And fill the extended list and call the methods:

TempDataList<TempData> tempDataList = new TempDataList<TempData>();
tempDataList.Add(new TempData(10, DateTime.UtcNow));
tempDataList.Add(new TempData(20, DateTime.UtcNow));
tempDataList.Add(new TempData(15, DateTime.MinValue));
tempDataList.Add(new TempData(25, DateTime.MaxValue));

Console.WriteLine(tempDataList.GetMaxTemp(DateTime.UtcNow.AddDays(-1), DateTime.UtcNow.AddDays(1)).Temp);
Console.WriteLine(tempDataList.GetMinTemp(DateTime.UtcNow.AddDays(-1), DateTime.UtcNow.AddDays(1)).Temp);