On Apr 11, 2013, at 11:46 AM, Richard Gildea wrote:

When I implemented the multidimensional slicing for flex arrays, I only did so because I required that functionality in code I was developing, not for the fun or challenge of emulating numpy arrays.

That's a good reminder to go back to the original question: what is the work-alike for slice assignment? Is set_selection() the best alternative?

I am unlikely to have time to add numpy-style assignment to slices in the near future, but if James, or indeed anyone else, requires and is willing to implement such behaviour, I'm sure Nat can grant you svn commit access in order to make the changes you require (providing that the changes play well with the rest of the cctbx code and Phenix, etc.).

I'm not sure I'd emulate numpy arrays in cctbx myself, as cool as they may be. It's usually better to try to find behavior that fits the rest of the library in "look and feel". However, if I had SVN commit privileges, I'd probably use them occasionally to fix problems I find or make enhancements that would aid my work.

James

On 11 April 2013 10:08, James Stroud <xtald00d@gmail.com> wrote:

On Apr 11, 2013, at 9:18 AM, Luc Bourhis wrote:

On 11 Apr 2013, at 09:49, James Stroud wrote:

It seems that flex arrays do not support slice assignment:

it would not be too difficult to code 1-dimensional slice assignment �but ...

On 11 Apr 2013, at 10:24, Graeme.Winter@Diamond.ac.uk wrote:

[...]

�����������array[k,:,:] = image.as_numpy_array()[y0:y1, x0:x1]

that's way more difficult!

In python this type of magic is fairly straightforward because the slice is just a tuple:

py> class Example(object):

... � def __setitem__(self, i, v):

... � � print "setting %s to %s" % (i, v)

...

py> e = Example()

py> e[5:6, 4, 8:9, "bob"] = 2

setting (slice(5, 6, None), 4, slice(8, 9, None), 'bob') to 2

This should actually be the case on the C side, too, not that it wouldn't take a few lines of code to build an iterator based on the slice.

But as a way to circumvent all of this magic with slices (which would be very cool, by the way), it might be easiest for the programmer (and somewhat intuitive for those familiar with flex) just to add a signature to set_selected() that uses a flex.grid to represent a slice because flex.grid already encapsulates the most useful aspects of slicing semantics.

Here is a prototype for the suggested behavior in python using ndarray as a back-end:

class Prototype(object):

� def __init__(self, data):

� � self.data = numpy.array(data)

� def __getitem__(self, i):

� � if isinstance (i, flex.grid):

� � � slices = [slice(*t) for t in zip(i.origin(), i.last())]

� � � return self.__class__(self.data[slices])

� � else:

� � � return self.__class__(self.data[i])

� def __setitem__(self, i, v):

� � if isinstance (i, flex.grid):

� � � slices = [slice(*t) for t in zip(i.origin(), i.last())]

� � � self.data[slices] = v

� � else:

� � � self.data[i] = v

� def __repr__(self):

� � return repr(self.data)

And here it is in action:

py> grd = flex.grid((1, 1), (3, 3)) �# <== selects [1:3, 1:3]

py> ary = Prototype(numpy.arange(25).reshape((5,5)))

py> ary

array([[ 0, �1, �2, �3, �4],

� � � �[ 5, �6, �7, �8, �9],

� � � �[10, 11, 12, 13, 14],

� � � �[15, 16, 17, 18, 19],

� � � �[20, 21, 22, 23, 24]])

py> ary[grd]

array([[ 6, �7],

� � � �[11, 12]])

py> ary[grd] = [[41, 42], [43, 44]]

py> ary[grd]

array([[41, 42],

� � � �[43, 44]])

py> ary

array([[ 0, �1, �2, �3, �4],

� � � �[ 5, 41, 42, �8, �9],

� � � �[10, 43, 44, 13, 14],

� � � �[15, 16, 17, 18, 19],

� � � �[20, 21, 22, 23, 24]])

James

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