# How do I determine which row my value change significantly

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new2matlab le 26 Nov 2019
Commenté : new2matlab le 26 Nov 2019
I'm looking to automate the process of finding where my column data changes from 375 (about the first 7 rows right now), as it starts decreasing constantly after that. Depending on the data loaded in, the change from a constant 375 can start anywhere from row 3 to row 8, so I'd like to detect where it begins. Thanks!
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### Réponse acceptée

Turlough Hughes le 26 Nov 2019
Modifié(e) : Turlough Hughes le 26 Nov 2019
You could find where data is not equal to 375 and then take the first index where this condition is true:
rowstart=min(find(data~=375))
Then your new data would be:
data2=data(rowstart:end);
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new2matlab le 26 Nov 2019
This is exactly what I needed. Thank you!

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### Plus de réponses (1)

TADA le 26 Nov 2019
Im assuming its roughly 375 and not exactly that value, otherwise go with Turlough Hughes' solution which is simpler.
The easiest method is to compare the values with tolerance to changes. You can define a threshold value that you would concider as significant reduction
% for the sake of this example I'm using 5% of the initial value (should be ~5% of 375)
threshold = 0.05*data(1);
sigDecMask = data < (data(1) - threshold);
startDecIdx = find(sigDecMask, 1, 'first');
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