Compute Percentage Change for TimeSeries

Question

Given a TimeSeries, ts, how can I compute the percentage change from one period to the next? Percentage change is calculated as (x[n] - x[n-1])/x[n-1] * 100.0. I've tried experimenting with MovingMap and pure functions but without success.

I can get the percentage change as a list of values with:

pc = MovingMap[(#[[2]] - #[[1]])/#[[1]] * 100.0 &, ts["Values"], {2}]

pc can then be plotted with ListLinePlot, but I'd really like to get back a TimeSeries object that can be plotted with DateListPlot.

Answer 1

It matters if your TimeSeries is RegularlySampledQ or not. If it is, then you can use

f = If[PossibleZeroQ[#1], Missing["Indeterminate"], 100 (#2 - #1) / #1]&;
MovingMap[f @@ #Values &, ts, {1, Right}]

otherwise you can use

MovingMap[f @@ #Values &, ts, {Quantity[2, "Events"], Right}]

where f is defined as in the previous code block. This time though, you are calculating a percentage difference that is not commensurate along the series, as it corresponds to different time spans.

Answer 2

Not too hard:

ts = TimeSeries[FinancialData["SBUX", "2016"]];
pc = TimeSeries[100. Differences[#]/Most[#] &[ts["Values"]], {Rest[ts["Dates"]]}];

DateListPlot[{ts, pc}, PlotLegends -> {"SBUX Close", "% change"}]