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

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

Answer 1

[Star Strider]

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:

Result =
     1     1
     2     6
     3     8
     4    13
     5    16
     6    20
     7    21
     8    24

[Benson Gou]

Thanks a lot for your great help.

Benson

[Star Strider]

As always, my pleasure!