Color based on (discrete) derivative of function

Question

I am making a very basic stock simulation. I want ListLinePlot to color my stock viewer based on whether the price went up or down from the previous price. Here is what I have:

RemoveScheduledTask[ScheduledTasks[]];
price = 100;
time = 0;
nextPrice := price += 2Random[]-1;
nextTime := time += Random[];
data = Table[{nextTime, nextPrice},{i,1,1000}];
Dynamic@ListLinePlot[
    data,
    ImageSize->1000,
    PlotRange->{{time-525,time+25}},
    ColorFunction->Function[If[Last@data[[-2]]<Last@data[[-1]], Green, Red]]
]
RunScheduledTask[
    data = Rest[data];
    AppendTo[data,{nextTime,nextPrice}];,
    .1
];

Currently this code makes the graph all one color (not what I want). Does anyone know how to implement the functionality that I want? Also any general code improvements are very welcome (I feel like the way I am pushing/popping data is inefficient).

Answer 1

This small modification to your code

• Seems to flicker less than your code
• Doesn't make use of Scheduled Tasks
• Stops when you click on the plot

---

price = 100;
 time = 0;
nextPrice := price += 2 Random[] - 1;
nextTime := time += Random[];
data = Table[{nextTime, nextPrice}, {i, 1, 1000}];
lastPriceChecked = price;
lastTimeChecked = time;
colorFunction[x_, y_] := 
  If[x == First[First[data]], lastPriceChecked = y;
   Return[Blue], If[y > lastPriceChecked, lastPriceChecked = y;
     Return[Green], lastPriceChecked = y;
     Return[Red]];];
cont = True;
DynamicModule[{}, 
 EventHandler[
  Dynamic@ListLinePlot[data, ImageSize -> 1000, 
    PlotRange -> {{time - 525, time + 25}}, 
    ColorFunction -> Function[{x, y}, colorFunction[x, y]], 
    AxesOrigin -> {time - 525, 100}], "MouseDown" :> (cont = False)]]
While[cont, (Pause[.1]; data = Rest[data];
   AppendTo[data, {nextTime, nextPrice}])];

Answer 2

I think I solved my own question, though there is almost certainly a "more proper" way to do it. Please post if you have a better way than this.

RemoveScheduledTask[ScheduledTasks[]];
price = 100;
time = 0;
nextPrice := price += 2 Random[] - 1;
nextTime := time += Random[];
data = Table[{nextTime, nextPrice}, {i, 1, 1000}];
lastPriceChecked = price;
lastTimeChecked = time;
colorFunction[x_, y_] := If[
   x == First[First[data]],
   lastPriceChecked = y;
   Return[Blue],
   If[
     y > lastPriceChecked,
     lastPriceChecked = y;
     Return[Green],
     lastPriceChecked = y;
     Return[Red]
     ];
   ];
Dynamic@ListLinePlot[data, ImageSize -> 1000, 
  PlotRange -> {{time - 525, time + 25}}, 
  ColorFunction -> Function[{x, y}, colorFunction[x, y]]]
RunScheduledTask[
  data = Rest[data];
  AppendTo[data, {nextTime, nextPrice}];
  , .1];