# using Matlab to plot density contour for scatter plot

조회 수: 211(최근 30일)
Keqiao Li 2015년 6월 30일
편집: Cris LaPierre 2020년 10월 29일
Hi guys, I'm trying to use Matlab to plot the density contour for the following scatter plot. The bins will be 1X1 box. Within my limited understanding the density contour should be indicated how many points fall into the bins(correct me if I'm wrong), but I still cannot find a way to do the density plot. Need some help to solve this problem. Thanks!

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### 채택된 답변

Mike Garrity 2015년 6월 30일
Scatter doesn't do any binning. It's showing each individual data element.
Perhaps this approach does what you want?
x = randn(1,1000);
y = randn(1,1000);
n = hist3([x', y']);
pcolor(n)
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Andrea Ackroyd 2018년 12월 3일
I am commenting on this old post because I am doing a very similar thing, but achieving some unexpected results.
I am making a histogram2 (tile view) of one dataset, which is time samples of two variables. On the same axes I plot a contour of a map which comes from different data (essentially a target map for the time based data which is in the histogram).
The unusual behaviour is that the colour scale of the hist2 appears to be affected by having the contour on the same axes.
If it is noteworthy, I am plotting the contour first, with a solid colour for all contour lines (not using colormap). Then I plot the histogram second.

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### 추가 답변(3개)

Walter Roberson 2015년 6월 30일
Assuming that your data starts at 0 and contains fractional values and is to be binned by 1 x 1, and that your coordinates are in X and Y,
xidx = 1 + floor(X(:));
maxxoff = max(xidx) - 1;
yidx = 1 + floor(Y(:));
maxyoff = max(yidx) - 1;
counts = accumarray([yidx, xidx], 1); %remember Y corresponds to rows
imagesc(counts, 'XData', 1/2+[0 maxxoff], 'YData', 1/2+[0 maxyoff]);
hold on
contour(1/2+(0:maxxoff), 1/2+(0:maxyoff), counts)
The 1/2 offsets have to do with referencing the centers of the boxes.
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Elena De Angelis 2016년 1월 14일
편집: Walter Roberson 2016년 1월 14일
Hi, I'm trying to do the same but my result is not what I expect, could someone tell me please what i'm doing wrong?
x = dNBR_filt_CHANGE;
y = NBR_post_CHANGE;
scatter(x,y,'r.')
hold on
[n,c] = hist3([x, y]);
contour(c{1},c{2},n)
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Hamdullah OZOGUL 2018년 2월 1일
You just have to transpose the n to have the correct order.
contour(c{1},c{2},n')

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Jos? Manuel Amigo 2017년 11월 11일
PCx = rand(2000,1); PCy = rand(2000,1);
bins = 50; Msize = 10;
[N C] = hist3([PCx,PCy],[bins bins]);
CX = C{1}; CY = C{2};
N2 = N; N2(N2 == 0) = []; Nunique = unique(N2);
colors = jet(length(Nunique));
for i = 1:length(PCx) if isnan(PCx(i)) PCxnew(i,1) = NaN; PCynew(i,1) = NaN; J(i,1) = NaN; else whichoneX = find(min(abs(CX - PCx(i))) == abs(CX - PCx(i))); PCxnew(i,1) = CX(whichoneX(1)); whichoneY = find(min(abs(CY - PCy(i))) == abs(CY - PCy(i))); PCynew(i,1) = CY(whichoneY(1)); J(i,1) = sub2ind([bins,bins],whichoneX(1),whichoneY(1)); end end
for i = 1:bins for j = 1:bins temp = sub2ind([bins,bins],i,j); Jthese = find(J == temp); if ~isempty(Jthese) Ntemp = N(temp); Nthis = find(Nunique == Ntemp); plot(PCx(Jthese),PCy(Jthese),'.','color',colors(Nthis,:),'Markersize',Msize); hold on; end end end hold off;
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Jos? Manuel Amigo 2017년 11월 11일
Sorry for the bad pasting. But if you copy-paste, it works

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