# Can the diff function go the opposite direction?

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Teddy Fisher on 18 Dec 2019
Commented: Steven Lord on 19 Dec 2019
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

Jeremy Marcyoniak on 18 Dec 2019
fliplr
or
flipud
and then run
diff

Teddy Fisher on 19 Dec 2019
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 Marcyoniak on 19 Dec 2019
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 on 19 Dec 2019
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.