Created
February 2, 2012 22:28
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Draw ROC Curve from two arrays
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function [Tps, Fps] = ROC(scores, labels) | |
%% Sort Labels and Scores by Scores | |
sl = [scores; labels]; | |
[d1 d2] = sort(sl(1,:)); | |
sorted_sl = sl(:,d2); | |
s_scores = sorted_sl(1,:); | |
s_labels = round(sorted_sl(2,:)); | |
%% Constants | |
counts = histc(s_labels, unique(s_labels)); | |
Tps = zeros(1, size(s_labels,2) + 1); | |
Fps = zeros(1, size(s_labels,2) + 1); | |
negCount = counts(1); | |
posCount = counts(2); | |
%% Shift threshold to find the ROC | |
for thresIdx = 1:(size(s_scores,2)+1) | |
% for each Threshold Index | |
tpCount = 0; | |
fpCount = 0; | |
for i = [1:size(s_scores,2)] | |
if (i >= thresIdx) % We think it is positive | |
if (s_labels(i) == 1) % Right! | |
tpCount = tpCount + 1; | |
else % Wrong! | |
fpCount = fpCount + 1; | |
end | |
end | |
end | |
Tps(thresIdx) = tpCount/posCount; | |
Fps(thresIdx) = fpCount/negCount; | |
end | |
%% Draw the Curve | |
% Sort [Tps;Fps] | |
x = Tps; | |
y = Fps; | |
% Interplotion to draw spline line | |
count = 100; | |
dist = (x(1) - x(size(x,2)))/100; | |
xx = [x(1):-dist:x(size(x,2))]; | |
% In order to get the interpolations, we remove all the unique numbers | |
[d1 d2] = unique(x); | |
uni_x = x(1,d2); | |
uni_y = y(1,d2); | |
yy = spline(uni_x,uni_y,xx); | |
% No value should exceed 1 | |
yy = min(yy, 1); | |
plot(x,y,'x',xx,yy); |
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