compare 2 consequtive columns ?

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]

even though the last column dosent chage , it should be displayed ?

[Fangjun Jiang]

You first and second column happen to be exactly the same. What if only one element changed, for example the second column is [3,10,9]'. Does it count as a change? What is the desired output? The number of changes? (in your case, 2)?

[Celestie Gladys]

@Fangjun JiangThe data I have changes the entire column, or it dosent change at all , so I asked about the entire column .

Answer 1

[Fangjun Jiang]

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

[Celestie Gladys]

@Fangjun JiangI require also to diaplay the changes in data like this ?

3 4 5

6 5 8

9 7 2

[Les Beckham]

data=[3 3 4 4 5 5
      6 6 5 5 8 8
      9 9 7 7 2 2];
unique(data', 'rows', 'stable')'

ans = 3×3

3 4 5 6 5 8 9 7 2

[Fangjun Jiang]

See update in the Answer

[Celestie Gladys]

@Fangjun Jiang does it work for type double ?as it isnt working for me , the above is dummy data ,index and index2

[Walter Roberson]

Those 0.0000 entries you see on output are locations where the output is not exactly 0, but is smaller than 0.0001 . If you were to configure your preferences for the variable browser to use "longg" format, then you would see the actual output more clearly.

Preferences -> Variables -> Format -> Default array format: long g

Preferences -> Command Window -> MATLAB Command Window Preferences -> Text display -> Numeric format: long g

The first of those controls the variable browser. The second of those controls "disp" and display of numbers triggered by not having a semi-colon after the computation.

[Celestie Gladys]

@Walter Roberson why does index=diff(data,1,2) dosent work and it suppose to generate [0,1]does it work on double ?

[Walter Roberson]

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