Mathematica-StackExchange-example-1
(See https://mathematica.stackexchange.com/a/273435/34008 .)
I am going to use QRMon because the workflow is easier to specify.
Procedure
Fit Quantile Regression (QR) curves:
Using small number of knots
At different probabilities (e.g. 0.25 and 0.75)
With different, low interpolation orders (e.g. 0, 1, 2)
Select QR parameters to extract the "near constant y" points.
Pick the points around produced regression quantile.
Using suitable pick range (e.g. 0.015)
Plot the original data points and the extracted ones.
Code
Import["https://raw.githubusercontent.com/antononcube/MathematicaForPrediction/master/MonadicProgramming/MonadicQuantileRegression.m"]data={{40.3595,0.001477},{40.9698,-0.007586},{38.0707,-0.013534},{39.5966,-0.003783},{42.6483,0.004349},{43.869,-0.00443},{39.7491,-0.006777},{42.4957,-0.00002},{43.7164,0.001113},{41.3513,-0.002448},{43.9453,0.000263},{46.463,0.004875},{44.7845,-0.000506},{43.4113,-0.000182},{43.7164,0.00617},{47.3022,0.004268},{45.2423,0.000829},{43.4875,0.005887},{46.3867,0.012643},{46.6156,0.003864},{46.7682,-0.001153},{48.2941,0.008921},{45.2423,0.013008},{48.2178,0.00532},{48.6755,0.004956},{48.0652,0.015718},{49.1333,0.011996},{50.4303,0.008152},{48.5992,0.013534},{50.8881,0.019198},{52.0325,0.014343},{50.4303,0.013088},{49.3622,0.016487},{52.7954,0.012117},{52.1851,0.010863},{50.7355,0.019683},{51.1169,0.025428},{53.4821,0.016649},{52.2614,0.011268},{47.9126,0.022273},{52.8717,0.025186},{53.1769,0.021828},{52.2614,0.017782},{55.6946,0.02644},{55.6946,0.024457},{51.1169,0.021221},{53.0243,0.025469},{58.2886,0.026804},{56.6864,0.023486},{56.6101,0.026683},{55.4657,0.035098},{56.839,0.030324},{56.6101,0.02381},{56.4575,0.028908},{58.3649,0.033561},{59.8145,0.026238},{56.4575,0.026521},{57.373,0.036797},{59.6619,0.035584},{59.967,0.02648},{58.5938,0.030203},{58.5175,0.037971},{60.3485,0.034896},{61.4929,0.030364},{60.0433,0.035705},{61.3403,0.035988},{61.1877,0.031052},{60.73,0.032671},{61.9507,0.0423},{62.8662,0.038254},{62.9425,0.029474},{60.9589,0.039508},{61.9507,0.046305},{65.155,0.034977},{62.7136,0.033803},{62.9425,0.045294},{65.155,0.043837},{63.4003,0.039063},{63.2477,0.043797},{68.4357,0.048166},{66.6046,0.048247},{64.621,0.042583},{65.155,0.049663},{67.5964,0.049299},{66.0706,0.046629},{66.2231,0.049097},{67.3676,0.05379},{68.2068,0.045456},{66.7572,0.042259},{65.5365,0.056541},{68.8171,0.054963},{71.5637,0.044646},{67.5201,0.043716},{67.5964,0.055773},{66.6809,0.056056},{67.5201,0.049299},{67.4438,0.049501},{66.7572,0.054437},{65.918,0.052981},{67.4438,0.053669},{66.2231,0.056218},{67.3676,0.050634},{65.4602,0.048288},{64.4684,0.055732},{66.0706,0.056541},{67.2913,0.049259},{65.3839,0.046629},{64.6973,0.059171},{64.0869,0.061315},{65.4602,0.052415},{62.8662,0.049501},{63.9343,0.058483},{63.5529,0.056703},{63.1714,0.050634},{61.4166,0.052779},{64.1632,0.055611},{63.2477,0.055449},{60.1196,0.054073},{58.8989,0.056825},{62.561,0.05205},{61.7218,0.0476},{59.8145,0.056784},{58.67,0.058079},{61.1115,0.052172},{58.2123,0.049097},{58.136,0.060304},{59.8907,0.063338},{58.5175,0.052576},{56.1523,0.0476},{56.6864,0.053062},{58.3649,0.052698},{55.6946,0.050351},{48.2941,0.053264},{55.2368,0.052415},{56.839,0.051848},{55.9998,0.052293},{55.0079,0.057148},{53.1769,0.049056},{54.1687,0.043999},{55.3894,0.053264},{54.8553,0.058888},{53.3295,0.048935},{50.2777,0.043999},{53.1006,0.056096},{53.2532,0.061032},{51.8799,0.046912},{49.8199,0.046184},{50.4303,0.050837},{52.5665,0.049259},{51.1169,0.046346},{49.1333,0.051929},{50.6592,0.045172},{49.1333,0.043069},{49.5911,0.051363},{50.0488,0.053264},{50.2777,0.04323},{47.6074,0.035341},{46.463,0.049866},{48.6755,0.058322},{48.6755,0.042098},{44.9371,0.037},{45.166,0.048773},{47.76,0.054802},{47.76,0.0476},{45.2423,0.048571},{44.3268,0.047155},{45.4712,0.048207},{44.8608,0.047843},{44.0216,0.054559},{43.1824,0.048652},{43.2587,0.042219},{43.6401,0.050756},{41.6565,0.054235},{41.7328,0.042502},{39.978,0.035867},{39.1388,0.051524},{42.4957,0.058928},{42.7246,0.046508},{39.444,0.040479},{41.6565,0.050027},{40.741,0.053628}} qrObj =
QRMonUnit[data]⟹
QRMonEchoDataSummary⟹
QRMonQuantileRegression[4, {0.25, 0.75, 0.85}, InterpolationOrder -> 0]⟹
QRMonPlot[];
qrObj =
QRMonUnit[data]⟹
QRMonQuantileRegression[1, {0.25, 0.75, 0.85}, InterpolationOrder -> 0]⟹
QRMonPlot[]⟹
QRMonPickPathPoints[0.015];
lsConstantYPoints = (qrObj⟹QRMonTakeValue)[0.75]
(*{{58.5175, 0.037971}, {61.9507, 0.0423}, {62.8662, 0.038254}, {60.9589, 0.039508}, {61.9507, 0.046305}, {62.9425, 0.045294}, {65.155, 0.043837}, {63.4003, 0.039063}, {63.2477, 0.043797}, {68.4357, 0.048166}, {66.6046, 0.048247}, {64.621, 0.042583}, {65.155, 0.049663}, {67.5964, 0.049299}, {66.0706, 0.046629}, {66.2231, 0.049097}, {67.3676, 0.05379}, {68.2068, 0.045456}, {66.7572, 0.042259}, {65.5365, 0.056541}, {68.8171, 0.054963}, {71.5637, 0.044646}, {67.5201, 0.043716}, {67.5964, 0.055773}, {66.6809, 0.056056}, {67.5201, 0.049299}, {67.4438, 0.049501}, {66.7572, 0.054437}, {65.918, 0.052981}, {67.4438, 0.053669}, {66.2231, 0.056218}, {67.3676, 0.050634}, {65.4602, 0.048288}, {64.4684, 0.055732}, {66.0706, 0.056541}, {67.2913, 0.049259}, {65.3839, 0.046629}, {64.6973, 0.059171}, {64.0869, 0.061315}, {65.4602, 0.052415}, {62.8662, 0.049501}, {63.9343, 0.058483}, {63.5529, 0.056703}, {63.1714, 0.050634}, {61.4166, 0.052779}, {64.1632, 0.055611}, {63.2477, 0.055449}, {60.1196, 0.054073}, {58.8989, 0.056825}, {62.561, 0.05205}, {61.7218, 0.0476}, {59.8145, 0.056784}, {58.67, 0.058079}, {61.1115, 0.052172}, {58.2123, 0.049097}, {58.136, 0.060304}, {59.8907, 0.063338}, {58.5175, 0.052576}, {56.1523, 0.0476}, {56.6864, 0.053062}, {58.3649, 0.052698}, {55.6946, 0.050351}, {48.2941, 0.053264}, {55.2368, 0.052415}, {56.839, 0.051848}, {55.9998, 0.052293}, {55.0079, 0.057148}, {53.1769, 0.049056}, {54.1687, 0.043999}, {55.3894, 0.053264}, {54.8553, 0.058888}, {53.3295, 0.048935}, {50.2777, 0.043999}, {53.1006, 0.056096}, {53.2532, 0.061032}, {51.8799, 0.046912}, {49.8199, 0.046184}, {50.4303, 0.050837}, {52.5665, 0.049259}, {51.1169, 0.046346}, {49.1333, 0.051929}, {50.6592, 0.045172}, {49.1333, 0.043069}, {49.5911, 0.051363}, {50.0488, 0.053264}, {50.2777, 0.04323}, {46.463, 0.049866}, {48.6755, 0.058322}, {48.6755, 0.042098}, {44.9371, 0.037}, {45.166, 0.048773}, {47.76, 0.054802}, {47.76, 0.0476}, {45.2423, 0.048571}, {44.3268, 0.047155}, {45.4712, 0.048207}, {44.8608, 0.047843}, {44.0216, 0.054559}, {43.1824, 0.048652}, {43.2587, 0.042219}, {43.6401, 0.050756}, {41.6565, 0.054235}, {41.7328, 0.042502}, {39.1388, 0.051524}, {42.4957, 0.058928}, {42.7246, 0.046508}, {39.444, 0.040479}, {41.6565, 0.050027}, {40.741, 0.053628}}*)ListPlot[{data, lsConstantYPoints}, PlotTheme -> "Detailed", PlotStyle -> {{GrayLevel[0.8], PointSize[0.02]}, {Red, PointSize[0.006]}}, PlotLegends -> {"data", "extracted"}]