[Numpy-discussion] Functions for indexing into certain parts of an array (2d)

Keith Goodman kwgoodman@gmail....
Sat Jun 6 13:46:52 CDT 2009


On Sat, Jun 6, 2009 at 11:30 AM, Fernando Perez <fperez.net@gmail.com> wrote:
> On Sat, Jun 6, 2009 at 12:09 AM, Robert Kern<robert.kern@gmail.com> wrote:
>> diag_indices() can be made more efficient, but these are fine.
>
> Suggestion?  Right now it's not obvious to me...

I'm interested in a more efficient way too. Here's how I plan to adapt
the code for my personal use:

def fill_diag(arr, value):
    if arr.ndim != 2:
        raise ValueError, "Input must be 2-d."
    idx = range(arr.shape[0])
    arr[(idx,) * 2] = value
    return arr

>> a = np.array([[1,2,3],[4,5,6],[7,8,9]])

>> a = fill_diag(a, 0)
>> a

array([[0, 2, 3],
       [4, 0, 6],
       [7, 8, 0]])

>> a = fill_diag(a, np.array([1,2,3]))
>> a

array([[1, 2, 3],
       [4, 2, 6],
       [7, 8, 3]])


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