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timeline - seasonality detection (III)
license: mit

This block is a continuation of this previous block. Both experiments how to detect if a timeline has a seasonality component, using a correlogram. This block explains why detrending the time serie before computing the correlogram is a must have.

Usages :

  • same usages as in this previous block
  • in the correlogram, detrending the time serie before computing the correlogram allows to detect very small seasonnality order of magnitude; detrending the time serie implies that coefficients of correlation for each lag no longer reflect any trend, and thus only reflect the seasonality component;
  • while using detrended time serie, increasing/decreasing trend has no longer any impact on the correlogram; chery on the cake, seasons are easier to detect.

Notes:

  • the previous block experiments season detection without detrending
  • another block experiments autocorrelation
  • another block experiments time series correlation
  • another block deals with the impact of seasonality when computing the trend of a timeline

Acknowledgments:

<!DOCTYPE html>
<meta charset="utf-8">
<style>
body {
position: relative;
background-color: #ddd;
margin: auto;
}
#under-construction {
display: none;
position: absolute;
top: 200px;
left: 300px;
font-size: 40px;
}
.controls {
position: absolute;
font: 11px arial;
}
#controls1 {
top: 300px;
left: 10px;
}
#controls2 {
top: 300px;
left: 450px;
}
#controls3 {
top: 300px;
right: 10px;
text-align: right;
}
#controls4 {
top: 5px;
right: 10px;
text-align: right;
}
.viz {
position: absolute;
background-color: white;
border-radius: 10px;
left: 5px;
}
.viz#timelines {
top: 5px;
}
.viz#correlation {
top: 355px;
}
.flow {
position: absolute;
font-size: 30px;
color: darkgrey;
top: 320px;
right: 435px;
}
.axis path,
.axis line {
fill: none;
stroke: black;
shape-rendering: crispEdges;
}
.axis text {
font-family: sans-serif;
font-size: 11px;
}
.grid>line, .grid>.intersect {
fill: none;
stroke: #ddd;
shape-rendering: crispEdges;
vector-effect: non-scaling-stroke;
}
.legend {
font-size: 12px;
}
.dot {
fill: steelblue;
stroke: white;
stroke-width: 3px;
}
.dot.original {
//fill: lightsteelblue;
fill-opacity: 0.3;
}
.dot.draggable:hover, .dot.dragging {
fill: pink;
cursor: ns-resize;
}
.timeline {
fill: none;
stroke: lightsteelblue;
stroke-width: 2px;
}
.timeline.original {
stroke-opacity: 0.3;
}
.timeline.draggable:hover, .timeline.dragging {
stroke: pink;
opacity: 1;
cursor: ns-resize;
}
.correlation-bar {
fill: grey;
}
</style>
<body>
<div id="timelines" class="viz">
<div id="controls1" class="controls">
update time serie with a seasonality's length of <a href="#" onclick="updateSeasonalityPeriod(2);">2</a> /<a href="#" onclick="updateSeasonalityPeriod(3);">3</a> / <a href="#" onclick="updateSeasonalityPeriod(4);">4</a> / <a href="#" onclick="updateSeasonalityPeriod(5);">5</a> / <a href="#" onclick="updateSeasonalityPeriod(6);">6</a> / <a href="#" onclick="updateSeasonalityPeriod(7);">7</a> / <a href="#" onclick="updateSeasonalityPeriod(8);">8</a> / <a href="#" onclick="updateSeasonalityPeriod(9);">9</a> / <a href="#" onclick="updateSeasonalityPeriod(10);">10</a> periods
</div>
<div id="controls2" class="controls">
<a href="#" onclick="changeSeasonOrderOfMagnitude(1.6);">increase</a> / <a href="#" onclick="changeSeasonOrderOfMagnitude(0.675);">decrease</a> seasonality's order of magnitude
</div>
<div id="controls3" class="controls">
<a href="#" onclick="changeTrend(1.6);">increase</a> / <a href="#" onclick="changeTrend(0.675);">decrease</a> timeline's trend
</div>
</div>
<div id="correlation" class="viz">
<div id="controls4" class="controls">
<label><input type='checkbox' onclick='handleDetrend(this);'>use detrended time serie</label>
</div>
</div>
<div id="flow" class="flow">&#8615;</div>
<div id="under-construction">
UNDER CONSTRUCTION
</div>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
var timeSerie = [];
var timeSerieForAutocor = [];
var randomness = [];
var currentSeasonLength = 4;
var currentSeasonOrderOfMagnitude = 8;
var currentTrend = 1.4;
var shouldDetrend = false;
var WITH_TRANSITION = true;
var WITHOUT_TRANSITION = false;
var duration = 500;
var NEW_RANDOMNESS = true;
var PRESERVE_RANDOMNESS = false;
var timelineVizDimension = {width: 960, height:340},
correlationVizDimension = {width: 960, height:160},
vizMargin = 5,
flowWidth = 20
legendHeight = 20,
xAxisLabelHeight = 10,
yAxisLabelWidth = 10,
correlationLeftShift = 110,
margin = {top: 20, right: 20, bottom: 20, left: 20},
timelineSvgWidth = timelineVizDimension.width - 2*vizMargin,
timelineSvgHeight = timelineVizDimension.height - 2*vizMargin - flowWidth/2,
correlationSvgWidth = correlationVizDimension.width - 2*vizMargin,
correlationSvgHeight = correlationVizDimension.height - 2*vizMargin - flowWidth/2,
timelineWidth = timelineSvgWidth - margin.left - margin.right - yAxisLabelWidth,
timelineHeight = timelineSvgHeight - margin.top - margin.bottom - xAxisLabelHeight - 1.5*legendHeight,
correlationWidth = correlationSvgWidth - margin.left - margin.right - yAxisLabelWidth - correlationLeftShift,
correlationHeight = correlationSvgHeight - margin.top - margin.bottom;
var drag = d3.behavior.drag()
.origin(function(d) { return d; })
.on("dragstart", dragStarted)
.on("drag", dragged1)
.on("dragend", dragEnded);
var x = d3.scale.linear()
.domain([0, 20])
.range([0, timelineWidth]);
var y = d3.scale.linear()
.domain([0, 50])
.range([0, -timelineHeight]);
var xCorrelation = d3.scale.linear()
.domain([1, 11])
.range([0, correlationWidth]);
var yCorrelation = d3.scale.linear()
.domain([-1, 1])
.range([0, -correlationHeight]);
var xAxisDef = d3.svg.axis()
.scale(x)
.ticks(20);
var yAxisDef = d3.svg.axis()
.scale(y)
.orient("left");
var xAxisCorrelationDef = d3.svg.axis()
.scale(xCorrelation)
.tickValues([2,3,4,5,6,7,8,9,10])
.tickFormat("");
var yAxisCorrelationDef = d3.svg.axis()
.scale(yCorrelation)
.ticks(5)
.orient("left");;
var svg = d3.select("#timelines").append("svg")
.attr("width", timelineSvgWidth)
.attr("height", timelineSvgHeight)
.append("g")
.attr("transform", "translate(" + [margin.left, margin.top] + ")");
var container = svg.append("g")
.attr("id", "graph")
.attr("transform", "translate(" + [yAxisLabelWidth, timelineHeight] + ")");
var grid = container.append("g")
.attr("class", "grid");
var intersects = [];
d3.range(1, x.invert(timelineWidth)+1, 1).forEach(function(a) { d3.range(5, y.invert(-timelineHeight)+5,5).forEach(function(b) { intersects.push([a,b])})});
grid.selectAll(".intersect")
.data(intersects)
.enter().append("path")
.classed("intersect", true)
.attr("d", function(d) { return "M"+[x(d[0])-1,y(d[1])]+"h3M"+[x(d[0]),y(d[1])-1]+"v3"});
container.append("text")
.attr("transform", "translate(" + [timelineWidth/2, -timelineHeight] + ")")
.attr("text-anchor", "middle")
.text("Timeline");
container.append("g")
.attr("class", "axis x")
.call(xAxisDef)
.append("text")
.attr("x", timelineWidth)
.attr("y", -6)
.style("text-anchor", "end")
.text("Time");
container.append("g")
.attr("class", "axis y")
.call(yAxisDef)
.append("text")
.attr("transform", "rotate(-90)")
.attr("x", timelineHeight)
.attr("y", 16)
.style("text-anchor", "end")
.text("Amount");
var timeline = container.append("path")
.datum(1)
.classed("timeline original", true)
.attr("d", line)
var timelineForAutocor = container.append("path")
.datum(2)
.classed("timeline for-autocor", true)
.attr("d", line)
var dotContainer = container.append("g")
.classed("dots", true);
svg = d3.select("#correlation").append("svg")
.attr("width", correlationSvgWidth)
.attr("height", correlationSvgHeight)
.append("g")
.attr("transform", "translate(" + [margin.left, margin.top] + ")");
container = svg.append("g")
.attr("id", "graph correlation")
.attr("transform", "translate(" + [yAxisLabelWidth + correlationLeftShift, correlationHeight] + ")");
var correlationTitle = container.append("text")
.attr("transform", "translate(" + [correlationWidth/2, -correlationHeight] + ")")
.attr("text-anchor", "middle")
.text("Correlogram");
grid = container.append("g")
.attr("class", "grid");
intersects = [];
d3.range(2, xCorrelation.invert(correlationWidth), 1).forEach(function(a) { d3.range(-1, yCorrelation.invert(-correlationHeight)+0.5,0.5).forEach(function(b) { intersects.push([a,b])})});
grid.selectAll(".intersect")
.data(intersects)
.enter().append("path")
.classed("intersect", true)
.attr("d", function(d) { return "M"+[xCorrelation(d[0])-1,yCorrelation(d[1])]+"h3M"+[xCorrelation(d[0]),yCorrelation(d[1])-1]+"v3"});
container.append("g")
.attr("class", "axis y")
.call(yAxisCorrelationDef);
var xAxisContainer = container.append("g")
.attr("class", "axis x");
xAxisContainer.append("line")
.attr("x1", 0)
.attr("y1", yCorrelation(0))
.attr("x2", correlationWidth)
.attr("y2", yCorrelation(0))
xAxisContainer.append("text")
.attr("transform", "translate("+[xCorrelation(2)-40,yCorrelation(-1)+15]+")")
.attr("text-anchor", "end")
.text("Coefficient of autocorrelation for ... ")
var xTicks = container.select(".axis.x").selectAll(".tick-label")
.data([2,3,4,5,6,7,8,9,10])
.enter()
.append("g")
.classed("tick-label", true)
.attr("transform", function(d) { return "translate("+[xCorrelation(d),0]+")"});
xTicks.append("line")
.attr("x1", 0)
.attr("y1", yCorrelation(0)-3)
.attr("x2", 0)
.attr("y2", yCorrelation(0)+4)
xTicks.append("text")
.attr("transform", "translate("+[0,yCorrelation(-1)+15]+")")
.attr("text-anchor", "middle")
.text(function(d) { return d+"-periods lag"});
var barContainer = container.append("g")
.attr("id", "bar-conatiner");
d3.csv("timeserie.csv", dottype, function(error, dots) {
updateTimeSeries(PRESERVE_RANDOMNESS);
updateDots(WITHOUT_TRANSITION);
updateTimelines(WITHOUT_TRANSITION);
updateAutocorrelations(WITHOUT_TRANSITION);
});
function dottype(d) {
d.x = +d.x;
d.y = +d.y+(+d.random);
timeSerie.push(d);
randomness.push(+d.random);
return d;
}
var line = d3.svg.line()
.x(function(d) { return x(d.x); })
.y(function(d) { return y(d.y); });
function updateSeasonalityPeriod(newSeasonLength) {
currentSeasonLength = newSeasonLength;
updateTimeSeries(NEW_RANDOMNESS);
updateDots(WITH_TRANSITION);
updateTimelines(WITH_TRANSITION);
updateAutocorrelations(WITH_TRANSITION);
}
function changeTrend(scale) {
currentTrend *= scale;
updateTimeSeries(PRESERVE_RANDOMNESS);
updateDots(WITH_TRANSITION);
updateTimelines(WITH_TRANSITION);
updateAutocorrelations(WITH_TRANSITION);
}
function changeSeasonOrderOfMagnitude(scale) {
currentSeasonOrderOfMagnitude *= scale;
updateTimeSeries(PRESERVE_RANDOMNESS);
updateDots(WITH_TRANSITION);
updateTimelines(WITH_TRANSITION);
updateAutocorrelations(WITH_TRANSITION);
}
function handleDetrend(cb) {
shouldDetrend = cb.checked;
updateTimeSeries(PRESERVE_RANDOMNESS);
updateDots(WITH_TRANSITION);
updateTimelines(WITH_TRANSITION);
updateAutocorrelations(WITH_TRANSITION);
}
function updateTimeSeries(reRandom) {
timeSerieForAutocor = [];
var intercept = 10;
var expected;
timeSerie.forEach(function(d,i) {
expected = intercept;
switch (i%currentSeasonLength) {
case 0: expected -= currentSeasonOrderOfMagnitude; break;
case (currentSeasonLength-1): expected += currentSeasonOrderOfMagnitude; break;
}
if (reRandom) {
randomness[i] = 3*(Math.random()-0.5);
}
d.y = expected + currentTrend*d.x + randomness[i];
timeSerieForAutocor.push({
x: d.x,
y: shouldDetrend? (d.y) : expected
})
})
updateTimeSerieForAutocor()
}
function updateTimeSerieForAutocor() {
timeSerieForAutocor = shouldDetrend? computeDetrendedSerie(timeSerie) : timeSerie;
}
function computeDetrendedSerie(serie) {
var serieLength = serie.length;
var periodMetrics = computePeriodMetrics(serieLength);
var valueMetrics = computeSerieMetrics(serie.map(function(d) { return d.y; }))
var correlationMetrics = computeCorrelationMetrics(periodMetrics,
valueMetrics,
serie.map(function(d) { return d.x; }),
serie.map(function(d) { return d.y; })
)
var detrended = [];
serie.forEach(function(d){
detrended.push({ x: d.x, y: d.y-d.x*correlationMetrics.correlatedTrend });
});
return detrended;
}
function computePeriodMetrics(periodCount) {
// compute metrics for the serie representing Time [1,2,...,periodCount]
var periodSum = periodCount*(periodCount+1)/2;
var squarePeriodSum = periodCount*(periodCount+1)*(2*periodCount+1)/6;
var mean = (periodCount+1)/2;
var variance = squarePeriodSum/periodCount - Math.pow(mean, 2);
var standardDeviation = Math.pow(variance, 0.5);
return {
countSum: periodSum,
squareCountSum: squarePeriodSum,
mean: mean,
variance: variance,
standardDeviation: standardDeviation
}
}
function computeSerieMetrics(serie) {
// compute metrics for the serie representing amounts
var serieLength = serie.length;
var valueSum = 0;
var squareValueSum = 0;
serie.forEach(function(d) {
valueSum += d;
squareValueSum += Math.pow(d, 2);
});
var mean = valueSum/serieLength;
var variance = squareValueSum/serieLength - Math.pow(mean, 2);
var standardDeviation = Math.pow(variance, 0.5);
return {
countSum: valueSum,
squareCountSum: squareValueSum,
mean: mean,
variance: variance,
standardDeviation: standardDeviation
}
}
function computeCorrelationMetrics(serie1Metrics, serie2Metrics, serie1, serie2) {
//compute correlation metrics of serie2 with regards to serie1
var serieLength = serie1.length;
var productSum = 0;
serie1.forEach(function(d1, i){
productSum += (d1)*(serie2[i]);
});
var covariance = productSum/serieLength - serie1Metrics.mean*serie2Metrics.mean;
var standardCodeviation = Math.pow(covariance, 0.5);
var correlationCoef = covariance/(serie1Metrics.standardDeviation*serie2Metrics.standardDeviation);
var correlatedTrend = covariance/serie1Metrics.variance;
var correlatedIntercept = serie2Metrics.mean - correlatedTrend*serie1.mean;
var invertedCorrelatedTrend = covariance/serie2Metrics.variance;
var invertedCorrelatedIntercept = serie1Metrics.mean - invertedCorrelatedTrend*serie2.mean;
return {
covariance: covariance,
standardCodeviation: standardCodeviation,
correlationCoefficient: correlationCoef,
correlatedTrend: correlatedTrend,
correlatedIntercept: correlatedIntercept,
invertedCorrelatedTrend: invertedCorrelatedTrend,
invertedCorrelatedIntercept: invertedCorrelatedIntercept
}
}
function updateDots(withTransition) {
var detrendedDots = dotContainer.selectAll(".dot.forAutocor")
.data(timeSerieForAutocor);
detrendedDots.enter()
.append("circle")
.classed("dot forAutocor", true)
.attr("r", 5)
.attr("cx", function(d) { return x(d.x); });
detrendedDots.transition()
.duration(withTransition? duration : 0)
.attr("cy", function(d) { return y(d.y); })
var dots = dotContainer.selectAll(".dot.original")
.data(timeSerie);
dots.enter()
.append("circle")
.classed("dot draggable original", true)
.attr("r", 5)
.attr("cx", function(d) { return x(d.x); })
.call(drag);
dots.transition()
.duration(withTransition? duration : 0)
.attr("cy", function(d) { return y(d.y); })
}
function updateTimelines(withTransition) {
timeline.transition()
.duration(withTransition? duration : 0)
.attr("d", line(timeSerie));
timelineForAutocor.transition()
.duration(withTransition? duration : 0)
.attr("d", line(timeSerieForAutocor));
}
function updateAutocorrelations(withTransition) {
var dataForAutocorrelationCoefficients = [];
var autocorCount = 9;
var lag = 2;
while (lag<=autocorCount+1) {
dataForAutocorrelationCoefficients.push({
lag: lag,
ySum: 0,
squareYSum: 0,
laggedYSum: 0,
squareLaggedYSum: 0,
yLaggedYSum: 0
})
lag++;
}
timeSerieForAutocor.forEach(function(tsData, tsIndex){
dataForAutocorrelationCoefficients.forEach(function(autocorData) {
if (tsIndex>=autocorData.lag) {
var laggedY = timeSerieForAutocor[tsIndex-autocorData.lag].y
autocorData.ySum += tsData.y;
autocorData.squareYSum += Math.pow(tsData.y, 2);
autocorData.laggedYSum += laggedY;
autocorData.squareLaggedYSum += Math.pow(laggedY, 2);
autocorData.yLaggedYSum += (tsData.y)*(laggedY);
}
})
})
var autocorrelationCoefficients = [];
dataForAutocorrelationCoefficients.forEach(function(autocorData) {
var autocorSerieLength = timeSerieForAutocor.length-autocorData.lag;
var yMean = autocorData.ySum/autocorSerieLength;
var laggedYMean = autocorData.laggedYSum/autocorSerieLength;
var yVariance = autocorData.squareYSum/autocorSerieLength - Math.pow(yMean, 2);
var laggedYVariance = autocorData.squareLaggedYSum/autocorSerieLength - Math.pow(laggedYMean, 2);
var yStdDev = Math.pow(yVariance, 0.5)
var laggedYStdDev = Math.pow(laggedYVariance, 0.5)
var yLaggedYCovariance = autocorData.yLaggedYSum/autocorSerieLength - yMean*laggedYMean;
var correlatedTrend = yLaggedYCovariance/(yVariance);
var correlatedIntercept = laggedYMean - correlatedTrend*yMean;
var autocorCoef = yLaggedYCovariance/(yStdDev*laggedYStdDev);
autocorrelationCoefficients.push({
autocorIndex: autocorData.lag,
autocorCoef: autocorCoef
});
});
bars = barContainer.selectAll(".correlation-bar")
.data(autocorrelationCoefficients);
bars.enter().append("path")
.classed("correlation-bar", true)
.attr("d", function(d) { return "M"+[xCorrelation(d.autocorIndex)-10,yCorrelation(0)]+"h20V"+yCorrelation(d.autocorCoef)+"h-20z" });
bars.transition()
.duration(withTransition? duration : 0)
.attr("d", function(d) { return "M"+[xCorrelation(d.autocorIndex)-10,yCorrelation(0)]+"h20V"+yCorrelation(d.autocorCoef)+"h-20z" });;
}
function dragStarted(d) {
d3.select(this).classed("dragging", true);
}
function dragged1(d) {
d.y += y.invert(d3.event.dy);
updateTimeSerieForAutocor()
updateDots(WITHOUT_TRANSITION);
updateTimelines(WITHOUT_TRANSITION);
updateAutocorrelations(WITHOUT_TRANSITION);
}
function dragEnded(d) {
d3.select(this).classed("dragging", false);
}
</script>
x y random
1 3 -1
2 10 -1
3 10 1
4 17 0
5 3 1
6 10 2
7 10 0
8 17 -1
9 3 0
10 10 0
11 10 -1
12 17 1
13 3 0
14 10 -1
15 10 1
16 17 0
17 3 2
18 10 1
19 10 -1
20 17 1
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