Removing Selected Lines With Multiple Studies

[AssetHound]

I have three studies plotting a line on the price chart. When a new bar comes in, each study does its calculations, and then plots a line extension from the old bar to the new bar. I do this using

drawLineRelative(-j,aWghtPrice[j],-(j-1),aWghtPrice[j-1],PS_SOLID,2,Color.blue,gID());

So, I end up with a bunch of different "lines." I come up with the tag identifier using

function gID() {return grID++};

Now I want to remove only the line from the second study and refresh it by redoing all the calculations and replotting. I could keep track of all the individual gID() numbers for this line and then removing the line with removeLine(...) inside some loop.

But, isn't there an easier way to remove just this one line? The clearLines() statement would remove all the lines -- even those from the other two studies. Right?

[eSignal_JasonK]

Hello AssetHound,

The first question that comes to mind is why are you using drawLineRelative() to plot each study? If you are calculating a value for each study that has a value for each bar it would be easier to plot the studies from the return statement rather that drawing a collection of line segments from bar to bar.

At any rate, to simplify the process of removing one of the drawnLine studies I would recommend assigning a series of unique tag names for each of the three drawnLine studies. Concatenate to the gID() number a string that identifies each set. For example, try using something like "LineA_" + gID() for the tag name parameter. Use "LineB_" and "LineC_" for the other two sets. Then you can add a Boolean function parameter for each of the 3 drawLine studies to control the display of each. When one is set to false from Edit studies you can prevent that drawLine study from being drawn. This process does require you to run a loop and call removeLine() to remove each segment. Changing the function parameter forces a reload of the study which will see a false value for the parameter and not redraw that corresponding line. Here's the basic idea for one of the the lines.

function preMain() {
    setStudyTitle("test");
    setPriceStudy(true);
    
    var fp1 = new FunctionParameter("bLineA", FunctionParameter.BOOLEAN);
        fp1.setName("Display Line A");
        fp1.setDefault(true);
}


function main(bLineA) {
    
    //  ... code logic for aWghtPrice array
    
    if (bLineA == true) {
        drawLineRelative(-j,aWghtPrice[j],-(j-1),aWghtPrice[j-1],PS_SOLID,2,Color.blue,"LineA_"+gID());
    }
    
    return;
}

function gID() {return grID++}; 

You wouldn't necessarily need to add the "LineA_" string to the tag name parameter in the above example. However, if you're using some other method to trigger the removal of the drawLine studies then you would need it so that a loop could be used that references the specific set of line segments corresponding to that tag name string and remove the desired set.

for (var i = 0; i <= grID; i++) {
    removeLine("LineA_"+i);
} 

[AssetHound]

That answered my question. I would need to use the loop and I'll look at the function parameter suggestion. Thanks.

Regarding drawLineRelative, I have to load all the bars and then look back to do a variety of calculations. The results of these calculations are plotted against the price, including prior bars, for comparisons on support and resistance. I tried return, but it didn't work like I needed -- but, you reminded me to try a couple of other things also. I still think I'll end up "drawing." Thanks.
-----------------------

The first question that comes to mind is why are you using drawLineRelative() to plot each study? If you are calculating a value for each study that has a value for each bar it would be easier to plot the studies from the return statement rather that drawing a collection of line segments from bar to bar.

[eSignal_JasonK]

You're most welcome. Thanks for the logic details, witch makes sense. I just wanted to make sure we weren't overlooking an easier solution.