How to use indexOf when you have a var variable?

Question

How to use indexOf when you have a var variable?

FranK Duc 121

Hello,

I have a list:

List<double> listCan = new List<double>() {};

I narrowed the index scope of my list :

int Lorest = totalBarIndex - ChartBars.GetBarIdxByX(chartControl, cursorPointX);
var Lowcursor = listCan.Skip(ChartBars.GetBarIdxByX(chartControl, cursorPointX)).Take(Lorest);

Than i got the Min from that new part of the list:

double Min = Lowcursor.Min();

I want the index from the new part Lowcursor.

If i int indexOfNumber = listCan.IndexOf(Min); ill get the Min from the entire list.

But i cant do int indexOfNumber = Lowcursor.IndexOf(Min);

How I can i get the index of Min from Lowcursor?

TY

Accepted answer

2 additional answers

Your answer

Answer 1

Michael Taylor 60,161

The question title is misleading here. This has nothing to do with var. Your question, if I understand correctly, is that you want to get the minimum value in Lowcursor which is an IEnumerable<double>. But you also want the index of that value. Not really sure why you need the index but unfortunately Min won't work here. Personally I think the easiest approach is to revert back to a good old looping construct.

public static class EnumerableExtensions
{
    public static int MinIndex<T> ( this IEnumerable<T> source ) where T: IComparable
    {            
        var minimumIndex = -1;
        var minimumValue = default(T);

        //IEnumerable<T> doesn't support array indexing and calling ToList or ToArray may be too expensive
        var index = 0;
        foreach (var value in source)
        {
            //If we haven't set a minimum yet OR the current value is less than our previous minimum
            if (minimumIndex == -1 || value.CompareTo(minimumValue) < 0)
            {
                minimumIndex = index;
                minimumValue = value;
            };

            //Next
            ++index;
        };

        return minimumIndex;
    }
}

Made this into an extension method so you can reuse it.

int minimumIndex = Lowcursor.MinIndex();
double minimumValue = Lowcursor.ElementAt(minimumIndex);

Of course if you can ensure that the values in the collection are unique or you don't really care which index you return if there are dups then you can use Min to find the minimum value and then iterate again to get the index but that is inefficient in many cases.

FranK Duc 121 Reputation points

2021-02-11T15:15:50.507+00:00

Hello Cool,

Min is not the problem. With double Min = Lowcursor.Min(); i get the answer i need which is 3688.75.

Yes, also Lowcursor is an IEnumerable<double>.
But i want to know which index is 3688.75. You see this is data from a chart. If i ask indexOf from listCan it returns the first index = to 3688.75 and not the index from the low of Lowcursor. Lowcursor is a part of data from listCan.

Is there a way to reshape that script without beeing a class?

TY
Michael Taylor 60,161 Reputation points

2021-02-11T15:28:46.367+00:00

Yes, the code I posted gives you that answer. It returns the index of the min value. This eliminates your need to use Min. Once you have the index you can get the actual value (the same thing Min returns) using ElementAt like I demoed. Hence you only make 1 pass over the data to get both the index and the minimum value. Try it and confirm you are getting the same exact answer (+ index) that you were originally getting with Min.

Yes you can use it without a class although I see 0 benefit in doing so. Just take the contents of the method body and drop it directly into your code and fix up any name conflicts.
FranK Duc 121 Reputation points

2021-02-11T15:33:47.383+00:00

I dont doubt your code, i just doubt my ability to make it fit. Its just that i am getting this error and dont know what to do with it.

NinjaScript File Error Code Line Column
FIFOajust5Min.cs The extension method must be defined in a top level static class, EnumerableExtensions is a nested class CS1109 459 26

Also

Michael Taylor 60,161

You are using NinjaScript so I assume it supports functions. Do this.

//New function
    int MinIndex ( IEnumerable<double> source )
    {            
        var minimumIndex = -1;
        var minimumValue = Double.MaxValue;

        var index = 0;
        foreach (var value in source)
        {
            //If we haven't set a minimum yet OR the current value is less than our previous minimum
            if (value.CompareTo(minimumValue) < 0)
            {
                minimumIndex = index;
                minimumValue = value;
            };
            //Next
            ++index;
        };
        return minimumIndex;
    }

//Now back in original code
//double Min = Lowcursor.Min();
int MinIndex = MinIndex(Lowcursor);
double Min = Lowcursor.ElementAt(MinIndex);

FranK Duc 121 Reputation points

2021-02-11T15:49:32.027+00:00

That part of the script wont do: int MinIndex ( IEnumerable<double> source ).

NinjaScript File Error Code Line Column
FIFOajust5Min.cs Class member declaration expected. 1085 4
}
NinjaScript File Error Code Line Column
FIFOajust5Min.cs Class, delegate, enum, interface, or struct expected. 1248 127

NinjaScript File Error Code Line Column
FIFOajust5Min.cs Extern alias declarations, using clauses, assembly/module attributes, or namespace/type declarations expected. 1249 9
Michael Taylor 60,161 Reputation points

2021-02-11T16:02:52.137+00:00

I don't know Ninjascript so does it have a class at the top of your file and one or more functions or is it just a bunch of C# code?

FranK Duc 121

I gave a reply in write and answer but it need to be review by a moderator. Its a script example of NT code. Looks like this:

namespace NinjaTrader.NinjaScript.Indicators
{
public class MyCustomIndicator6 : Indicator
{

    protected override void OnStateChange()
    {
        if (State == State.SetDefaults)
        {
            Description                                 = @"Enter the description for your new custom Indicator here.";
            Name                                        = "MyCustomIndicator6";
            Calculate                                   = Calculate.OnBarClose;
            IsOverlay                                   = true;

        }
        else if (State == State.Configure)
        {
        }
    }

    protected override void OnBarUpdate()
    {



           }

    protected override void OnRender(ChartControl chartControl, ChartScale chartScale)
    {


    }

Answer 2

Here's and example of Ninjacode structure:

My script fit in OnRender class, i tried to input your code above in the between :

//This namespace holds Indicators in this folder and is required. Do not change it.
namespace NinjaTrader.NinjaScript.Indicators
{
// Your code here is crashing
public class MyCustomIndicator6 : Indicator
{

Here's an example how it looks. Its a test code i use.

region Using declarations

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media;
using System.Xml.Serialization;
using NinjaTrader.Cbi;
using NinjaTrader.Gui;
using NinjaTrader.Gui.Chart;
using NinjaTrader.Gui.SuperDom;
using NinjaTrader.Gui.Tools;
using NinjaTrader.Data;
using NinjaTrader.NinjaScript;
using NinjaTrader.Core.FloatingPoint;
using NinjaTrader.NinjaScript.DrawingTools;

endregion

//This namespace holds Indicators in this folder and is required. Do not change it.
namespace NinjaTrader.NinjaScript.Indicators
{
public class MyCustomIndicator6 : Indicator
{

    protected override void OnStateChange()
    {
        if (State == State.SetDefaults)
        {
            Description                                 = @"Enter the description for your new custom Indicator here.";
            Name                                        = "MyCustomIndicator6";
            Calculate                                   = Calculate.OnBarClose;
            IsOverlay                                   = true;
            DisplayInDataBox                            = true;
            DrawOnPricePanel                            = true;
            DrawHorizontalGridLines                     = true;
            DrawVerticalGridLines                       = true;
            PaintPriceMarkers                           = true;
            ScaleJustification                          = NinjaTrader.Gui.Chart.ScaleJustification.Right;
            //Disable this property if your indicator requires custom values that cumulate with each new market data event. 
            //See Help Guide for additional information.
            IsSuspendedWhileInactive                    = true;

        }
        else if (State == State.Configure)
        {
        }
    }

    protected override void OnBarUpdate()
    {

}

    protected override void OnRender(ChartControl chartControl, ChartScale chartScale)
    {


    }
}

}

region NinjaScript generated code. Neither change nor remove.

namespace NinjaTrader.NinjaScript.Indicators
{
public partial class Indicator : NinjaTrader.Gui.NinjaScript.IndicatorRenderBase
{
private MyCustomIndicator6[] cacheMyCustomIndicator6;
public MyCustomIndicator6 MyCustomIndicator6()
{
return MyCustomIndicator6(Input);
}

    public MyCustomIndicator6 MyCustomIndicator6(ISeries<double> input)
    {
        if (cacheMyCustomIndicator6 != null)
            for (int idx = 0; idx < cacheMyCustomIndicator6.Length; idx++)
                if (cacheMyCustomIndicator6[idx] != null &&  cacheMyCustomIndicator6[idx].EqualsInput(input))
                    return cacheMyCustomIndicator6[idx];
        return CacheIndicator<MyCustomIndicator6>(new MyCustomIndicator6(), input, ref cacheMyCustomIndicator6);
    }
}

}

namespace NinjaTrader.NinjaScript.MarketAnalyzerColumns
{
public partial class MarketAnalyzerColumn : MarketAnalyzerColumnBase
{
public Indicators.MyCustomIndicator6 MyCustomIndicator6()
{
return indicator.MyCustomIndicator6(Input);
}

    public Indicators.MyCustomIndicator6 MyCustomIndicator6(ISeries<double> input )
    {
        return indicator.MyCustomIndicator6(input);
    }
}

}

namespace NinjaTrader.NinjaScript.Strategies
{
public partial class Strategy : NinjaTrader.Gui.NinjaScript.StrategyRenderBase
{
public Indicators.MyCustomIndicator6 MyCustomIndicator6()
{
return indicator.MyCustomIndicator6(Input);
}

    public Indicators.MyCustomIndicator6 MyCustomIndicator6(ISeries<double> input )
    {
        return indicator.MyCustomIndicator6(input);
    }
}

}

endregion

Michael Taylor 60,161 Reputation points

2021-02-11T16:25:46.787+00:00

Place the code like so:

public class MyCustomIndicator6 : Indicator { private int MinIndex ( IEnumerable<double> source ) { var minimumIndex = -1; var minimumValue = Double.MaxValue; var index = 0; foreach (var value in source) { //If we haven't set a minimum yet OR the current value is less than our previous minimum if (value.CompareTo(minimumValue) < 0) { minimumIndex = index; minimumValue = value; }; //Next ++index; }; return minimumIndex; } //The rest of your code }
FranK Duc 121 Reputation points

2021-02-11T16:31:21.997+00:00

No i get a bunch of NinjaScript File Error Code Line Column
FIFOajust5Min.cs Class, delegate, enum, interface, or struct expected. 48 10

Too bad we just cant make a list out of Lowcursor to manipulate the new list.

That part wont pass ( IEnumerable<double> source )
Michael Taylor 60,161 Reputation points

2021-02-11T16:42:25.087+00:00

The error indicates that it is expecting a class or type definition and isn't finding it. Please post the code around the line 48 where the compiler is complaining.

The IEnumerable<double> isn't the issue here. You're using System.Collections.Generic which defines both List<T> and IEnumerable<T>.
FranK Duc 121 Reputation points

2021-02-11T16:57:59.257+00:00

This is compiling, now how do i get the index? i try to print minimumIndex but nothing showup on output. Probably it need int minimumIndex = Lowcursor.MinIndex();
double minimumValue = Lowcursor.ElementAt(minimumIndex); somewhere. But where?

Lowcursor is in OnRender class. But minimumIndex and minimumValue will return error:

NinjaScript File Error Code Line Column
FIFOajust5Min.cs' System.Collections.Generic.IEnumerable <double> 'does not contain a definition for' MinIndex 'and no extension method' MinIndex 'accepting a first argument of type' System.Collections.Generic.IEnumerable <double> 'was not found (is a using directive or assembly reference missing?) CS1061 523 36
Michael Taylor 60,161 Reputation points

2021-02-11T17:02:24.54+00:00

As I demoed in the sample code earlier, where you're currently calling your Lowcursor.Min() function, comment it out. In its place put the 2 lines of code. The first one gets the index (which was your original ask). The second one sets the Min variable you were originally setting by calling Lowcursor.Min() to now get it from the index that was returned. However since you cannot use an extension method the call to MinIndex has to change.

int minimumIndex = MinIndex(Lowcursor); double Min = Lowcursor.ElementAt(minimumIndex);
FranK Duc 121 Reputation points

2021-02-11T17:10:18.21+00:00

Its returning the right minimum but not the right index.

Probably because there is shift between the listCan and Lowcursor. I have to investigate this.
FranK Duc 121 Reputation points

2021-02-11T17:12:03.103+00:00

Thank you for the help by the way.
I learned a lot.
Michael Taylor 60,161 Reputation points

2021-02-11T17:14:11.9+00:00

I assume you mean the index in listCan that you assume matches the index in Lowcursor. They definitely won't line up if you do any sort of manipulation of the listCan to produce Lowcursor including Where clauses. If you need to map manipulated values in Lowcursor back to their original item in listCan then you're going to have to add data to relate the 2 values. A double will no longer be sufficient for this. But that is a different question that you can post on if you need help with it.
FranK Duc 121 Reputation points

2021-02-11T17:25:47.9+00:00

When your scipt look for the index.
It search from left to right? 0 to ...

Can we do the opposite looking from (...) to 0, that way i will just need to reverse the number to get the right index. I mean subtract from total number of bars in the chart.

Is it possible?
Michael Taylor 60,161 Reputation points

2021-02-11T17:38:14.98+00:00

It goes left to right because IEnumerable is a forward only set of items. If you want to get the highest index then you'll still have to go left to right but you can change the comparison logic from (value < minValue) to (value <= minValue). This will cause the function to find the highest index instead.

Answer 3

FranK Duc 121

Not the highest index, still want the index of lowest price.

Its a chart it goes from index 0 (left side of the chart) to number of bars in the chart (right side) or ChartBars.FromIndex to ChartBars.ToIndex.

I need to convert the number of bars in listCan to number of bars in Lowcursor.

Michael Taylor 60,161 Reputation points

2021-02-11T18:01:19.95+00:00
"Not the highest index, still want the index of lowest price."

Yes the code does that. You said you wanted to go from right to left (or highest index to lowest). You cannot do that with IEnumerable but if you change from < to <= then you accomplish the same thing. The function will return the highest index of the item that has the lowest price. It is equivalent to enumerating right to left instead of left to right.

var items = new [] { 10, 20, 10, 30 }; var indexOnList = MinIndex(items); // Returns 2, version that uses <= for comparison var indexOnReversedList = MinIndex(items.Reverse()); // Returns 2, there is no Reverse method, making it up, version that used the original < for comparison

As for the ChartBarts and index stuff you should post a different question for that as this post was about getting the index of the minimum value.
FranK Duc 121 Reputation points

2021-02-11T18:26:26.603+00:00

I got it i found a solution.
This problem is solve. Now i have another bug but its unrelated.

Thank you for your patience Cool
Michael Taylor 60,161 Reputation points

2021-02-11T18:48:11.647+00:00

Excellent, glad to hear you got it working.
FranK Duc 121 Reputation points

2021-02-12T15:53:30.257+00:00

Dont know if you are still available but i have an issue.

Will it be possible to resuse the code you gave me to list all double in listCan and use the values in my OnRender class.

I created a private list to manipulate data from class OnBarUpdate.
I try to use listCan in OnRender class but if i try:

foreach(var item in listCan)
{
Print("CAN"+listCan);
}

It return CANSystem.Collections.Generic.List`1[System.Double] and i am unable to find the bug i have.

By doing var sumP = listCan.Skip(foundIndex).Take(Trest); i thought i could get only the prices after foundIndex (500) so price 500 to ----> 1000

But var sumP = listCan.Skip(foundIndex).Take(Trest); return the wrong prices. That means listCan prices are wrong too.

So somewhere the prices have gone throught some transformation i am not aware.

Any idea what i could do?
Michael Taylor 60,161 Reputation points

2021-02-12T15:55:36.17+00:00

Please post this as a separate question as it isn't related to the question you asked for this post.
FranK Duc 121 Reputation points

2021-02-12T16:43:38.23+00:00

new question
https://learn.microsoft.com/en-us/answers/questions/271252/how-to-get-list-prices-from-ienumerableltdoublegt.html

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How to use indexOf when you have a var variable?

2 additional answers

endregion

region NinjaScript generated code. Neither change nor remove.

endregion

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