# diff not working on a vector of values

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Jason on 24 Apr 2024
Commented: Jason on 24 Apr 2024
Is there a reason why I cant calculate the difference between each of these values (x1)
This is the code Im using
[x1,y1]=SpotFind_NXC(app,ax2); %my function to locate x,y coordinates of spots in an image
x1
class(x1)
xdiff=abs(diff(x1))
and the command window:
x1 =
98.00
97.68
97.75
98.32
221.00
220.99
221.32
221.32
344.00
343.99
344.33
344.25
ans =
'double'
Unrecognized function or variable 'diff'.
2nd Question, once it works, how can I group these into "similar values". so ideally I would want the median (or mean) of the 1st group (98.00, 97.68. 97.75, 98.32), and then the median of the 2s group around 221 and the 3rd group around 344.
Thanks
Jason
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### Accepted Answer

Cris LaPierre on 24 Apr 2024
There is nothing about the code you have shared that would prohibit you from using diff. For some reason, it is not on your MATLAB path. You may need to reset your path using restoredefaultpath
x1 = [98.00 97.68 97.75 98.32 221.00 220.99 221.32 221.32 344.00 343.99 344.33 344.25]';
xdiff=abs(diff(x1))
xdiff = 11x1
0.3200 0.0700 0.5700 122.6800 0.0100 0.3300 0 122.6800 0.0100 0.3400
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Not sure what typical values will be. You could use discretize or histcounts to bin your data. Here's one approach assuming your data is sorted.
% use xdiff to determine
nbins = sum(xdiff>mean(xdiff))+1
nbins = 3
[N,edges,bin] = histcounts(x1,nbins)
N = 1x3
4 4 4
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edges = 1x4
80 170 260 350
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bin = 12x1
1 1 1 1 2 2 2 2 3 3
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splitapply(@mean,x1,bin)
ans = 3x1
97.9375 221.1575 344.1425
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Jason on 24 Apr 2024
Thankyou for the answer.

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### More Answers (1)

Matt J on 24 Apr 2024
x=[ 98.00
97.68
97.75
98.32
221.00
220.99
221.32
221.32
344.00
343.99
344.33
344.25];
G=findgroups(round(x,-1));
Medians=splitapply(@median,x,G)
Medians = 3x1
97.8750 221.1600 344.1250
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Jason on 24 Apr 2024
Thankyou Matt, I love this findgroups approach. Is it possible to define a value that defines whether its ina group or not
Thanks

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