Find places before or after zeros in vector

Hi MATLAB-Community,

I'm searching for an elegant way to mark the places before and after zeros in a Vector.

e.g.:

a = 0 0 0 1 1 1 0 0 1 1 1 0 1 1 1 0 1 1 0

before = 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0

after = 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0

Has anybody an Idea that can help me with that Problem?

Thanks in advance!

Cheers

Christian

Answer 1

[Ive J]

a       = [0 0 0 1 1 1 0 0 1 1 1 0 1 1 1 0 1 1 0];
before  = [0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0];
after   = [0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0];

da = [diff(a), 0];
bcheck = circshift(da > 0, 1);
acheck = da < 0;

all(bcheck == before)

ans = logical
   1

all(acheck == after)

ans = logical
   1

This may not cover leading and trailing zeros, though before and after zeros may not make sense in that case.

[Christian S.]

Perfect, thank you very much!