Following some excellent advice on this forum, I have created an app where I plot columns to represent the strength and position of lines in difraction spectra for a number of materials

The heart of the code is

f1[l_, lower_, 
  upper_] := (If[
   Length[Select[b[[l]], #[[1]] > lower && #[[1]] < upper &]] > 0, 
   Black, Red])


f[l_, u_] := (
    colarr = f1[#, l, u] &  /@ Range[num];

    ListPointPlot3D[
        res, Filling -> Bottom, ColorFunctionScaling -> False, 
   ColorFunction -> Function[{x, y, z}, colarr[[x]]  ]
              ]   
  )
Manipulate[
 f[ll, uu], {ll, 0, 19.9, Appearance -> "Labeled"}, {uu, .1, 20, 
  Appearance -> "Labeled"}]

b is a list of lists containing the pairs or points where b[[1]] [[1]] gives the position of the line
res is another list derived from b like this

res = {};
Do[  AppendTo[res, Map[Prepend[i], b[[i]]]], {i, num}];

It is a list of triplets giving the 3D points

The idea is if the material has enough points within lower and upper bounds in the y axis it will be a different colour from the points for other materials This works great providing I want to plot a couple of hundred points but it just does not function when I want to plot 2000.

SO MY QUESTION IS :- HOW DO I IMPROVE THE PERFORMANCE?

One thing that I have thought of is that these are not really 2000 independent points. The are rows of points along each value of the x axis. Each row has typically 10 points, all of which will be the same colour. I wondered if I could create a single Line object ( with the 10 vertical lines in) , whose locartion and size would remain absolutely constant, but I would want to change the colour(of the whole Line) as the values of ll and uu were changed in the manipulate.

I am going to experiment with this and maybe this will be even slower. Has anyone got any better ideas?

Thanks

Graham