# compare 2 consequtive columns ?

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Celestie Gladys on 26 Jan 2023
Commented: Walter Roberson on 26 Jan 2023
for example this 3x6 matrix
3 3 4 4 5 5
6 6 5 5 8 8
9 9 7 7 2 2
i want to compare two columns and display any changes in column , diplay number of times the changes occur .
the output should be
3 4 5
6 5 8
9 7 2
number times : 2
Celestie Gladys on 26 Jan 2023
@Fangjun JiangThe data I have changes the entire column, or it dosent change at all , so I asked about the entire column .

Fangjun Jiang on 26 Jan 2023
Edited: Fangjun Jiang on 26 Jan 2023
data=[3 3 4 4 5 5
6 6 5 5 8 8
9 9 7 7 2 2];
index=diff(data,1,2)
index = 3×5
0 1 0 1 0 0 -1 0 3 0 0 -2 0 -5 0
index2=any(index)
index2 = 1×5 logical array
0 1 0 1 0
output=sum(index2)
output = 2
OutData=data(:,[true,index2])
OutData = 3×3
3 4 5 6 5 8 9 7 2
Walter Roberson on 26 Jan 2023
diff() works fine on double, but your data might not be exactly what you think it is.
format long g
x = rand(1,10);
x(3) = x(2);
x(7) = x(6)*(1+eps);
x.'
ans = 10×1
0.891461741281098 0.631347191045054 0.631347191045054 0.516064708409579 0.824509730719412 0.720280713237283 0.720280713237283 0.96542744133625 0.503147047594 0.108609798103955
entry 3 should be exactly the same as entry 2, so we should see an exact 0 difference there
entry 7 displays exactly the same as entry 6, but is different in the final bits, so we should not see an exact 0 difference there
diff(x,1,2).'
ans = 9×1
-0.260114550236044 0 -0.115282482635475 0.308445022309833 -0.104229017482129 1.11022302462516e-16 0.245146728098968 -0.462280393742251 -0.394537249490044