[Numpy-discussion] addressing a submatrix (original) (raw)

Martin Wiechert martin.wiechert at gmx.de
Wed Jun 14 05:14:17 EDT 2006

Hi list,

is there a concise way to address a subrectangle of a 2d array? So far I'm using

A [I] [:, J]

which is not pretty and more importantly only works for reading the subrectangle. Writing does not work. (Cf. session below.)

Any help would be appreciated.

Thanks, Martin

In [1]:a = zeros ((4,4))

In [2]:b = ones ((2,2))

In [3]:c = array ((1,2))

In [4]:a [c] [:, c] = b

In [5]:a Out[5]: array([[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]])

In [6]:a [:, c] [c] = b

In [7]:a Out[7]: array([[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]])

In [8]:a [c, c] = b

In [9]:a Out[9]: array([[0, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0]])

In [10]:a [c] [:, c] Out[10]: array([[1, 0], [0, 1]])

In [11]: