[Numpy-discussion] Run length encoding of an ndarray
Stefan van der Walt
Tue Oct 2 08:36:42 CDT 2007
On Tue, Oct 02, 2007 at 01:36:02PM +0100, Michael Hoffman wrote:
> I am trying to do a type of run-length encoding of a 2D array by axis. I
> have an array of values arranged along two axes, state and position.
> These are many (180, 30000) uint8 arrays.
> I would like to have a list of tuples like
> (state, start_pos, end_pos, values)
> only separating out a set of values into a new tuple if they are all the
> same value in a run of at least 10 cells.
This snippet does run-length encoding for one row.
x = N.array([1,1,1,1,1,1,1,1,1,1,0,0,2,2,9,9,9,9,9,9,9,9,9,9])
pos, = N.where(N.diff(x) != 0)
pos = N.concatenate((,pos+1,[len(x)]))
rle = [(a,b,x[a]) for (a,b) in zip(pos[:-1],pos[1:])]
[(0, 10, 1), (10, 12, 0), (12, 14, 2), (14, 24, 9)]
Maybe you can use that as a starting point.
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