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Hi

I need a method to split my x axis into intervals and estimate the average for each one of the intervals. The plots are polynomial curves, if that helps.

Any suggestion?

Thank you

Adam Danz
on 19 May 2019

Edited: Adam Danz
on 20 May 2019

This is relatively straight forward with histcounts() and splitapply().

% Create fake data

x = randi(1000,1,1000); %doesn't have to be sorted

y = rand(size(x));

% Define the edges of your x data

% There's lots of ways to do this - this is just 1 example.

binWidth = 100; %how wide is each bin?

edges = min(x) : binWidth : max(x);

% determine which bin each x element is in

[~, ~, hbin] = histcounts(x,[edges,inf]);

% Get mean of y within each bin

% Here I ignore NaN values, too.

binMean = splitapply(@(x)mean(x,'omitna'),y,hbin);

To interpret the results, binMean(n) is the mean for all y values where x is greater or equal to edges(n) and less than edges(n+1).

To plot the data, the bins, and display the average values per bin above the axis:

figure

plot(x,y,'b.')

hold on

plot([edges;edges],[0,1],'k')

text(edges+binWidth/2, ones(size(edges)), strsplit(num2str(binMean,.1)), ...

'VerticalAlignment', 'Bottom', 'HorizontalAlignment', 'Center')

% * binMean must be a row vector

Adam Danz
on 20 May 2019

Glad I could help.

The 2nd input to text() indicates where along the y axis your labels should go. In my example I simply used y=1 for all labels because my data didn't span beyond 1. You could just do this

ylim([-0.5, 2])

text(edges+binWidth/2, ones(size(edges))*max(ylim()), ......

also, see the "rotation" text property. It might look better to rotate the labels by 90 deg.

Also, to draw the lines across your entire axis,

plot([edges;edges],[min(ylim()), max(ylim())],'k')

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