Can the diff function go the opposite direction?

Hello,

As I understand diff it goes either left to right along rows or up to down a column. Is there a way to make diff do the same thing it currently does but go right to left or down to up?

Thanks,

Teddy

Answer 1

[Jeremy]

sure, flip your matrix with

fliplr

or

flipud

and then run

diff

[Teddy Fisher]

Hi, thanks for your answer, that is good to know.

I should clarify my case a bit, because I tried that and it does work.

However, for my case I am trynig to use diff to find the indices of stand alone values in a logical array. To do this, I am trying to find where the diff of a cell is either 1 or -1 in both directions, i.e. a single 1 in a series of 0s or vice versa. So using these flip commands changes the indices.

Is there another way to do this?

[Jeremy]

Wouldn't you fliplr the original array, call diff on it, and then flip the resulting array again to get what you want?

[Steven Lord]

So you want to detect when the abs-olute diff-erence between adjacent elements is exactly 1?

If you know that your data only contains 0 and 1 (or false and true) it's even easier than using abs and diff.

x = randi([0 1], 1, 10)
d = [x(1:end-1) ~= x(2:end), 0]

[x; d]

Each element of d is true when the corresponding element of x differs from the next element in x. I set the last element of d to false because it doesn't make sense to ask if the last element is different from the nonexistent next-after-the-last element.