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2D Histogram Matrix

version 1.0.0.0 (1.21 KB) by Kangwon Lee
Returns a matrix of number of points in each bins defined by two vectors.

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Updated 18 Jul 2006

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Editor's Note: This file was selected as MATLAB Central Pick of the Week

function mHist = hist2d ([vY, vX], vYEdge, vXEdge)
2 Dimensional Histogram
Counts number of points in the bins defined by vYEdge, vXEdge.
size(vX) == size(vY) == [n,1]
size(mHist) == [length(vYEdge) -1, length(vXEdge) -1]

EXAMPLE

mYX = rand(100,2);
vXEdge = linspace(0,1,10);
vYEdge = linspace(0,1,20);
mHist2d = hist2d(mYX,vYEdge,vXEdge);

nXBins = length(vXEdge);
nYBins = length(vYEdge);
vXLabel = 0.5*(vXEdge(1:(nXBins-1))+vXEdge(2:nXBins));
vYLabel = 0.5*(vYEdge(1:(nYBins-1))+vYEdge(2:nYBins));
pcolor(vXLabel, vYLabel,mHist2d); colorbar

Cite As

Kangwon Lee (2020). 2D Histogram Matrix (https://www.mathworks.com/matlabcentral/fileexchange/1487-2d-histogram-matrix), MATLAB Central File Exchange. Retrieved .

Comments and Ratings (25)

Aaron Swan

MATLAB provides the function hist3 to generate bivariate (2D) histograms

Very useful but a little buggy.

Depending on you bin sizes you use, the program can crash due to machine rounding errors.

Change lines 25 & 26 in Plot2dHist to read:
vLabelX = linspace(rMinX+0.5*rDeltaX, rMaxX-0.5*rDeltaX, size(mHist2D,2));
vLabelY = linspace(rMinY+0.5*rDeltaY, rMaxY-0.5*rDeltaY, size(mHist2D,1));

fixes this.

Pearl

Woot Master

Leiguang Wang: You've misunderstood this code. At line 38 vColFound will be an empty matrix if line 36 doesn't find any values within the given x bin. isempty is the correct function to call here. Your preferred code would break if the y bin spanned 0 and only had counts exactly at 0 in that bin.

I do have a small issue though. The handling of values exactly at the bin edges is different in x and y. Line 36 reads:

vColFound = vCol((vRow > rRowLB) & (vRow <= rRowUB));

To match what histc does in y this should really have >= and < rather than > and <=. This is most likely not a problem in the majority of cases.

Leiguang Wang

very fast. but has a little bug.
in line 38
expression: if (~isempty(vColFound))

this is always true, since even (vColFound == 0)
doesn't mean vColFound is empty .
i think
if (abs(vColFound(:))~= 0) is preferable.

tudor t

the function has a bug that I was unable to locate, it was faster to write my own function; it affects the last row and the first column, (or viceversa)

for instance with this data
x = [
0 0 1 1 0 0.4 0.6 0.6 0 0.4 0.4 0.4 0.6 0.6 1 1];
y = [
0 1 0 1 0.6 0.4 0 0.6 0.4 0 0.6 1 0.4 1 0.4 0.6];

but although size(x,2) = size(y,2) = 16
when checking sum(sum(bin_2D)) one gets 9 !

Christof Konig Beatty

Lines 12 and 13 (where nEdgeX and nEdgeY are defined) are actually useless and can be omitted.

Daniel Mark

Hi Kangwon Lee and Iain Strachan
Thank you all:)

Iain Strachan

If the histogram spacing is regular and assumed to be divided between the minimum and maximum values, then one can use the useful property of the sparse(i,j,vals) command, that it sums the values assigned to repeated indices, to do a 2d histogram very quickly, something like this...

function m = mk2dhist(vals,n)
% function m=mk2dhist(vals,n)
% make a 2 d histogram nxn
vX = vals(:,1);
vY = vals(:,2);
vX = round((n-1)*(vX - min(vX))/(max(vX)-min(vX)))+1;
vY = round((n-1)*(vY - min(vY))/(max(vY)-min(vY)))+1;
m = full(sparse(vX,vY,ones(length(vX),1)));

I can't yet think of a simple way to exploit this for non-evenly spaced histograms though

Denny Jackson

Workes exactly like I wanted.
Very user friendly.

Evan Variano

Works well. It's Short and sweet

Nikolaus Correll

IMO one needs to swap lines 27 and 28 if the bins in x and y are not equally spaced. If this is not the case, the version as is gives rotated histograms.

Jos Groot

Just what I needed.

Andrew Meijers

Excellent, it did exactly what it said it would. Great for contouring dense scatter fields.

Martin Müller

Explicit specification of edges is inconvinient. Why do the vectors have to be passed as a matrix? Plotting of the result often doesnt work. Plot is not a 2d bar chart as expected.

Dimitri Shvorob

Thank you!

Ali H.

Does exactly what it says on the tin! Easy to use, fast, simple, great.

Jim Jazz

Useful

guiot etienne

simple and fast

Kevin Aptowicz

Great!

luiz Loures

practical

H Chen

Nicely done!

R Corbett

Exactly what I needed

Tony Kim

This is what I wanted. Why MATLAB doesn't have this kind of command, I don't understand.

Mark Ward

It does what you'd expect :-)
A surface plot instead of contours would be a useful option. I know - I should add this myself!

Updates

1.0.0.0

Code cleaning

Adding a separate plotting function

MATLAB Release Compatibility
Created with R11.1
Compatible with any release
Platform Compatibility
Windows macOS Linux
Acknowledgements

Inspired: 2-Dimensional Histogram