maintaining relative positions of each elements of the resulting array after applying Union()

Question

Aditya Tan 2018-12-29

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https://ww2.mathworks.cn/matlabcentral/answers/437550-maintaining-relative-positions-of-each-elements-of-the-resulting-array-after-applying-union

评论： Aditya Tan 2019-1-3

采纳的回答： Walter Roberson

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Hi,

I have a question regarding Matlab's Union.

Suppose I have the following two string arrays.

x1 = ["assets"; "fixed asset"; "total assets"; "short-term bank loans";                         "revenue"; "equity"];
x2 = ["assets"; "fixed asset"; "total assets";                          "long-term bank loans"; "revenue"; "equity"];

If I do this

x3 = union(x1,x2,'stable')

Then the result is

x3 = ["assets"; "fixed asset"; "total assets"; "short-term bank loans"; "revenue"; "equity"; "long-term bank loans"]; % result

But what I want is

x3 = ["assets"; "fixed asset"; "total assets"; "short-term bank loans"; "long-term bank loans"; "revenue"; "equity"]; % what I want

Any help or suggestions are appreciated. Thank you very much.

Aditya

PS This is not a homework problem.

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Walter Roberson 2018-12-29

union is a set operation so if duplicates appear later then they would have to be eliminated .I suspect that is not what you want .

II suspect what you want is "Compare corresponding pairs of elements .if they are the same use one copy . If they are different use the first then the second ."

Is that more accurate ? If it is then it can be done efficiently with some logical indexing.

Aditya Tan 2018-12-29

Hi Walter,

I suppose yes. I had thought this operation can be done efficiently with Union. The resulting elements from the Union() operation are correct--it's just their positions that are not.

Then, are you suggesting to achieve this with a loop instead? Thanks.

Aditya

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Answer 1

Walter Roberson 2018-12-29

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https://ww2.mathworks.cn/matlabcentral/answers/437550-maintaining-relative-positions-of-each-elements-of-the-resulting-array-after-applying-union#answer_354282

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x3 = [x1.'; x2.'];
mask = [true(1, length(x1)); x3(1,:) ~= x3(2,:)];
x3 = x3(mask);

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Aditya Tan 2018-12-29

Thanks. Aditya

Aditya Tan 2019-1-3

Hi Walter,

Thanks for your help last week. I actually oversimplified my problem and still couldn't figure it out. Perhaps, if you have time, please take a look at the following thread:

https://www.mathworks.com/matlabcentral/answers/438034-compare-elements-and-shift-the-elements-up-or-down-based-on-matching-previous-or-next-elements

Thanks. Aditya

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