How to quickly find the index of each integer in an ascend array?

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Benson Gou 2020-3-19

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评论： Star Strider 2020-3-19

Hi, All,

I have an array which has an ascend integers. Now I want to find the index of the first integer in this array. For example, I have an array A = [1 1 1 1 1 2 2 3 3 3 3 3 4 4 4 5 5 5 5 6 7 7 7 8 8]. I want to find out the index of each integer.

Integer Index

[1 1

2 6

3 8

4 13

5 16

6 20

7 21

8 24];

Thanks a lot.

Benson

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采纳的回答

Star Strider 2020-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/511645-how-to-quickly-find-the-index-of-each-integer-in-an-ascend-array#answer_420823

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Use the unique function:

A = [1 1 1 1 1 2 2 3 3 3 3 3 4 4 4 5 5 5 5 6 7 7 7  8 8];
[Au,firstidx] = unique(A(:), 'stable');
Result = [Au, firstidx]

producing:

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Benson Gou 2020-3-19

Thanks a lot for your great help.

Benson

Star Strider 2020-3-19

As always, my pleasure!

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