Remove traces from graph with loops

hello I calculated the average concentration of my elements then I made a graph (name graph 0) which represents the concentration according to the dates. now I would like on my graph 0 to delete the elements whose average concentration is <18 so I made a loop as in the figure (I'm sorry for not putting the codes directly I'm new with Igor) but when I executes my function it doesn't execute the condition for me, only it recalculates the average can you help me please

The figure is below

Screen shots are ... rather impossible to read well if at all.

Please learn how to post your code. Use the Insert Code Snippet button. Copy the code from the procedure window in Igor Pro and paste it directly into the Code Snippet window.

#pragma rtGlobals=3     // Use modern global access method and strict wave access.

Function analysededonnees(dates,elements)

    loadwave/W/J
    // loadwave utilisé pour télécharger
    // les donées ; /W: utilisé pour  importer
    // les données avec leurs noms; /J:indique que
    // le fichier utilise le format texte
    // délimité.

End

Function modifier(elements)
    wave elements
    wave dates
    display elements vs dates
    print mean (elements)


    variable i

    For (i=0;i<31;i= i+1)

        if (mean elements[i]<18)
            removefromgraph element


        Endif
    Endfor
End

 

Reading this and both previous topics it seems that you want to "blank-out" data points on a graph that fall below a certain threshold. All of the commands that you need to accomplish this were already mentioned. If this is not what you want then you need to explain it in more detail.

There are several problems with the code above and I don't know what you want do with "mean()", but maybe try this one: 

function modifier(wave yy, wave xx, variable threshold)
    display yy vs xx
   
    yy = yy[p] < threshold ? NaN : yy[p]
end

 

In your case you would execute from the command line:

modifier(elements, dates, 18)

Yy, xx, and threshold are just place-holders for whatever you want to pass to the function. To understand what is otherwise happening, please execute 

DisplayHelpTopic "? :"