From d83c9b524622286d4dcd35d1233dfc722511a5be Mon Sep 17 00:00:00 2001 From: "Robert C. Helling" Date: Sun, 10 Jan 2021 00:12:41 +0100 Subject: Indicate goodness of fit of regression line The goodness of fit of a regression line is the percentage of the variance of the y values that is explained by the dependence on the x values. Set the alpha value of the regression line to this goodness of fit. Further, set the width of the regression line to a standard deviation of the values from the regression line valies. Signed-off-by: Robert C. Helling --- stats/statsview.cpp | 76 ++++++++++++++++++++++++++++++++--------------------- stats/statsview.h | 8 +++--- 2 files changed, 51 insertions(+), 33 deletions(-) diff --git a/stats/statsview.cpp b/stats/statsview.cpp index 5583643d7..405677e56 100644 --- a/stats/statsview.cpp +++ b/stats/statsview.cpp @@ -723,13 +723,14 @@ void StatsView::QuartileMarker::updatePosition() x + quartileMarkerSize / 2.0, y); } -StatsView::RegressionLine::RegressionLine(double a, double b, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) : - item(createItemPtr(scene)), +StatsView::RegressionLine::RegressionLine(double a, double b, double width, QBrush brush, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) : + item(createItemPtr(scene)), xAxis(xAxis), yAxis(yAxis), - a(a), b(b) + a(a), b(b), width(width) { item->setZValue(ZValues::chartFeatures); - item->setPen(pen); + item->setPen(Qt::NoPen); + item->setBrush(brush); } void StatsView::RegressionLine::updatePosition() @@ -738,21 +739,16 @@ void StatsView::RegressionLine::updatePosition() return; auto [minX, maxX] = xAxis->minMax(); auto [minY, maxY] = yAxis->minMax(); - double y1 = a * minX + b; - double y2 = a * maxX + b; - - // If not fully inside drawing region, do clipping. - if ((y1 < minY || y1 > maxY || y2 < minY || y2 > maxY) && fabs(a) > 0.0001) { - // Intersections with y = minY and y = maxY lines - double intersect_x1 = (minY - b) / a; - double intersect_x2 = (maxY - b) / a; - if (intersect_x1 > intersect_x2) - std::swap(intersect_x1, intersect_x2); - minX = std::max(minX, intersect_x1); - maxX = std::min(maxX, intersect_x2); - } - item->setLine(xAxis->toScreen(minX), yAxis->toScreen(a * minX + b), - xAxis->toScreen(maxX), yAxis->toScreen(a * maxX + b)); + + QPolygonF poly; + poly << QPointF(xAxis->toScreen(minX), yAxis->toScreen(a * minX + b + width)) + << QPointF(xAxis->toScreen(maxX), yAxis->toScreen(a * maxX + b + width)) + << QPointF(xAxis->toScreen(maxX), yAxis->toScreen(a * maxX + b - width)) + << QPointF(xAxis->toScreen(minX), yAxis->toScreen(a * minX + b - width)) + << QPointF(xAxis->toScreen(minX), yAxis->toScreen(a * minX + b + width)); + QRectF box(QPoint(xAxis->toScreen(minX), yAxis->toScreen(minY)), QPoint(xAxis->toScreen(maxX), yAxis->toScreen(maxY))); + + item->setPolygon(poly.intersected(box)); } StatsView::HistogramMarker::HistogramMarker(double val, bool horizontal, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis) : @@ -784,9 +780,15 @@ void StatsView::addHistogramMarker(double pos, const QPen &pen, bool isHorizonta histogramMarkers.emplace_back(pos, isHorizontal, pen, &scene, xAxis, yAxis); } -void StatsView::addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis) +void StatsView::addLinearRegression(double a, double b, double res2, double r2, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis) { - regressionLines.emplace_back(a, b, QPen(Qt::red), &scene, xAxis, yAxis); + QColor red = QColor(Qt::red); + red.setAlphaF(r2); + QPen pen(red); + QBrush brush(red); + brush.setStyle(Qt::SolidPattern); + + regressionLines.emplace_back(a, b, sqrt(res2), brush, &scene, xAxis, yAxis); } // Yikes, we get our data in different kinds of (bin, value) pairs. @@ -1025,12 +1027,21 @@ static bool is_linear_regression(int sample_size, double cov, double sx2, double return true; // can't happen, as we tested for sample_size above. } -// Returns the coefficients [a,b] of the line y = ax + b -// If case of an undetermined regression or one with infinite slope, returns [nan, nan] -static std::pair linear_regression(const std::vector &v) +struct regression_data { + double a,b; + double res2, r2; +}; + +// Returns the coefficients a,b of the line y = ax + b +// as well as the variance of the residuals (averaged residual squared) as res2 +// and r^2 = 1.0 - variance of data / res2 which is the fraction of the variance of +// the data that is explained by the linear regression. +// If case of an undetermined regression or one with infinite slope, returns {nan, nan, 0.0, 0.0} + +static struct regression_data linear_regression(const std::vector &v) { if (v.size() < 2) - return { NaN, NaN }; + return { .a = NaN, .b = NaN, .res2 = 0.0, .r2 = 0.0}; // First, calculate the x and y average double avg_x = 0.0, avg_y = 0.0; @@ -1051,10 +1062,15 @@ static std::pair linear_regression(const std::vector 0.0 ? 1.0 - res2 / sy2 : 1.0; + return { .a = a, .b = b, .res2 = res2 / v.size(), .r2 = r2 }; } void StatsView::plotScatter(const std::vector &dives, const StatsVariable *categoryVariable, const StatsVariable *valueVariable) @@ -1084,10 +1100,10 @@ void StatsView::plotScatter(const std::vector &dives, const StatsVariabl series->append(dive, x, y); // y = ax + b - auto [a, b] = linear_regression(points); - if (!std::isnan(a)) { + struct regression_data reg = linear_regression(points); + if (!std::isnan(reg.a)) { auto [minx, maxx] = axisX->minMax(); auto [miny, maxy] = axisY->minMax(); - addLinearRegression(a, b, minx, maxx, miny, maxy, xAxis, yAxis); + addLinearRegression(reg.a, reg.b, reg.res2, reg.r2, minx, maxx, miny, maxy, xAxis, yAxis); } } diff --git a/stats/statsview.h b/stats/statsview.h index fbf51d46e..198ded14f 100644 --- a/stats/statsview.h +++ b/stats/statsview.h @@ -9,6 +9,7 @@ #include #include #include +#include struct dive; struct StatsBinner; @@ -117,11 +118,12 @@ private: // A regression line struct RegressionLine { - std::unique_ptr item; + std::unique_ptr item; StatsAxis *xAxis, *yAxis; double a, b; // y = ax + b + double width; void updatePosition(); - RegressionLine(double a, double b, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis); + RegressionLine(double a, double b, double width, QBrush brush, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis); }; // A line marking median or mean in histograms @@ -134,7 +136,7 @@ private: HistogramMarker(double val, bool horizontal, QPen pen, QGraphicsScene *scene, StatsAxis *xAxis, StatsAxis *yAxis); }; - void addLinearRegression(double a, double b, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis); + void addLinearRegression(double a, double b, double res2, double r2, double minX, double maxX, double minY, double maxY, StatsAxis *xAxis, StatsAxis *yAxis); void addHistogramMarker(double pos, const QPen &pen, bool isHorizontal, StatsAxis *xAxis, StatsAxis *yAxis); StatsState state; -- cgit v1.2.3-70-g09d2