compare 2 consequtive columns ?

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Celestie Gladys 2023-1-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1901320-compare-2-consequtive-columns

评论： Walter Roberson 2023-1-26

采纳的回答： Fangjun Jiang

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

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Fangjun Jiang 2023-1-26

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 2023-1-26

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

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采纳的回答

Fangjun Jiang 2023-1-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1901320-compare-2-consequtive-columns#answer_1157140

编辑：Fangjun Jiang 2023-1-26

在 MATLAB Online 中打开

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

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Celestie Gladys 2023-1-26

@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 2023-1-26

在 MATLAB Online 中打开

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

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