Jagged array in cython

Question

If I have a jagged list in python like

jagged = [[1],[2,3]]

how can I declare it as an array using numpy and cython? Is it possible somehow? I know the following syntax, but it won't do, as it gives only a 1D array.

cdef numpy.ndarray[np.float_t] jagged

Answer 1

Numpy arrays (both in and out of Cython) are typically rectangular. You don't say what you're trying to do with the jagged array, but you might be able to use:

http://docs.scipy.org/doc/numpy/reference/maskedarray.html

or:

http://docs.scipy.org/doc/scipy/reference/sparse.html

As for the 1-dimensional part of your question, you're wanting the ndim param (mode='c' can speed things up if you won't be getting any order='F' arrays):

cdef numpy.ndarray[DTYPE_t, ndim=2, mode='c'] somearray