How to count the number of times that values changes?

A=[1 1 1 2 1 3 3 1 1]' I want to get:

B=[NaN 0 0 1 2 3 3 4 4]'

The second and third values of B are 0 because A doesn't change value. Fourth value is 1 because A changes value. Fifth value is 2 because A changes value again. And so on...

Answer 1

[Stephen23]

A = [1;1;1;2;1;3;3;1;1]

A = 9×1

1 1 1 2 1 3 3 1 1

B = [NaN;cumsum(diff(A)~=0)]

B = 9×1

NaN 0 0 1 2 3 3 4 4

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Answer 2

[Mario Malic]

Hello,

This should do the trick.

B = [NaN; cumsum(diff(A) ~= 0)]';

[Stephen23]

A = [1 1 1 2 1 3 3 1 1]';
B = [NaN, cumsum(diff(A) ~= 0)]'

Error using horzcat
Dimensions of arrays being concatenated are not consistent.

[Mario Malic]

Thanks Stephen, fixed it now.