How can I do 1-D interpolation with INTERP1 to find the nearest value to the left of the point (i.e. a zero-order hold curve) in MATLAB?

Question

MathWorks Support Team 2012-8-16

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https://ww2.mathworks.cn/matlabcentral/answers/101237-how-can-i-do-1-d-interpolation-with-interp1-to-find-the-nearest-value-to-the-left-of-the-point-i-e

编辑： MathWorks Support Team 2015-2-6

I want to do 1-D interpolation such that the interpolated value for a given point will be equal to the value of the point which is closest and on the left (i.e., smalller than the given point) of the data set. 'Nearest' method of INTERP1 function does not work as I want since the nearest point might be to the right of (i.e., larger than) the given point.

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Answer 1

MathWorks Support Team 2013-10-18

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https://ww2.mathworks.cn/matlabcentral/answers/101237-how-can-i-do-1-d-interpolation-with-interp1-to-find-the-nearest-value-to-the-left-of-the-point-i-e#answer_110585

The easiest and probably fastest way to achieve that is to use histc respectively histcounts.

Code example:

% create some example data
x=linspace(0,10,100);
y=sin(x);
% those are the query points
xi=linspace(1,9,50);
% use histcounts to get the locations
% of the nearest left neighbours
[~,~,bin]=histcounts(xi,x);
plot(x,y,'b*')
hold on
plot(xi,y(bin),'r*')