From 8b886c758fe0bb92589ed2922686cda2ec383661 Mon Sep 17 00:00:00 2001
From: grokify <johncwang@gmail.com>
Date: Mon, 4 Apr 2022 12:31:58 -0700
Subject: [PATCH] feat: data/timeseries: add `TimeSeries.TimeSeriesMonthXOX()`

---
 data/timeseries/time_series_month_xox.go | 44 ++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 data/timeseries/time_series_month_xox.go

diff --git a/data/timeseries/time_series_month_xox.go b/data/timeseries/time_series_month_xox.go
new file mode 100644
index 0000000..bb0edd2
--- /dev/null
+++ b/data/timeseries/time_series_month_xox.go
@@ -0,0 +1,44 @@
+package timeseries
+
+import "strings"
+
+func (ts *TimeSeries) TimeSeriesMonthYOY() TimeSeries {
+	return ts.TimeSeriesMonthXOX(-1, 0, 0, "YoY")
+}
+
+func (ts *TimeSeries) TimeSeriesMonthQOQ() TimeSeries {
+	return ts.TimeSeriesMonthXOX(0, -3, 0, "QoQ")
+}
+
+func (ts *TimeSeries) TimeSeriesMonthXOX(years, months, days int, suffix string) TimeSeries {
+	tsm := ts.ToMonth(true)
+	tsXOX := NewTimeSeries(tsm.SeriesName)
+	suffix = strings.TrimSpace(suffix)
+	if len(suffix) > 0 {
+		if len(tsm.SeriesName) > 0 {
+			tsXOX.SeriesName += " " + suffix
+		} else {
+			tsXOX.SeriesName = suffix
+		}
+	}
+	tsXOX.IsFloat = true
+	tsXOX.Interval = tsm.Interval
+	times := tsm.TimeSlice(true)
+	times.SortReverse()
+
+	for _, dt := range times {
+		dtThis := dt
+		dtPast := dt.AddDate(years, months, days)
+		tiThis, err := tsm.Get(dtThis)
+		if err != nil {
+			panic("cannot find this time")
+		}
+		tiPast, err := ts.Get(dtPast)
+		if err != nil {
+			continue
+		}
+		tsXOX.AddFloat64(dtThis, (tiThis.Float64()-tiPast.Float64())/tiPast.Float64())
+	}
+
+	return tsXOX
+}