# how to find blocks of values within array where difference is less than X for a specific number of values without losing the last value?

4 views (last 30 days)
Oscar on 19 Nov 2015
Answered: Oscar on 19 Nov 2015
Hi, I am up for a problem which I cannot totally solve.
Imagine I have an array: testtimes=[0.2 1.2 1.202 1.205 1.209 1.8 2.1 2.6 2.604 2.606 3.601 3.603 3.605]; Now I need to find all series of values where the difference between values is less than 0.01 for at least three testtimes in a row. So for now I did this:
if true
% code
end
% reference = 0.01
% isitesttimes=diff(testtimes); belowBIthreshold=(isitesttimes<reference);
% belowBIthreshold = [false, belowBIthreshold, false];
% edges = diff(belowBIthreshold);
% rising = find(edges==1); falling = find(edges==-1); spanWidth = falling - rising; wideEnough = spanWidth >= 3;
% startPos = rising(wideEnough);
% endPos = falling(wideEnough)-1;
% allInSpan = cell2mat(arrayfun(@(x,y) x:1:y, startPos, endPos, 'uni', false))
allInSpan = 2 3 4
Which means that on position 2,3,4 in testtimes the values are postioned which have a difference less than 0.01. However, the correct answer in this example would be 2,3,4,5 (since also position 5 has a difference of less than 0.01 compared to the one on position 4) (apart from that 8,9,10,11,12,13 should also be in the answer but that has to do (I guess) with the cut-off/Span-Width of 3).
Preferably I would get a variable which has per row the positions of the testtimes, so:
Answer = 2,3,4 % 8,9,10 % 11,12,13 (because between 10 and 11 there is more than 0.01 difference)
Can somebody help me out because I don't know how to solve that also position 5 is in the answer?
Regards

Thorsten on 19 Nov 2015
The code computes the differences between positions such that the final position is dropped. Just add it, using y+1:
allInSpan = cell2mat(arrayfun(@(x,y) x:1:y+1, startPos, endPos, 'uni', false))

Ingrid on 19 Nov 2015
if you also want the last value why don't you just write
endPos = falling(wideEnough);
instead of what you currently have
endPos = falling(wideEnough)-1;
to solve your other problem of not giving the last two arrays you need to put
wideEnough = spanWidth >= 2;
just check the output of belowBIthreshold to see why this will give you three consecutive threshold agreements

Thorsten on 19 Nov 2015
The code computes the differences between positions such that the final position is dropped. Just add it, using y+1:
allInSpan = cell2mat(arrayfun(@(x,y) x:1:y+1, startPos, endPos, 'uni', false))

Oscar on 19 Nov 2015
Thanks everyone :) sometimes it is so simple you don't see it :)

Oscar on 19 Nov 2015
Thanks everyone :) sometimes it is so simple you don't see it :)

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