On Fri, Jan 30, 2009 at 21:54, Scott Sinclair wrote:

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Maybe an optional val= keyword?

What would be the advantage compared to fill ? I would guess ones and zeros are special because those two values are special (they can be defined for many types, as neutral elements for + and *),

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2009/1/30 David Cournapeau : Neal Becker wrote:

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A nit, but it would be nice if 'ones' could fill with a value other than

I couldn't find the numpy fill function, until my tiny brain realized you meant the ndarray method:

http://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.fill.html

Cheers, Scott

Is fill function has any advantage over ones(size)*x ? -- Cheers, Grissiom

Right now there are 2 options to create an array of constant value: 1) empty (size); fill (val) 2) ones (size) * val 1 has disadvantage of not being an expression, so can't be an arg to a function call. Also probably slower than create+fill @ same time 2 is probably slower than create+fill @ same time Now what would be _really_ cool is a special array type that would represent a constant array without wasting memory. boost::ublas, for example, has this feature.

On 1/30/2009 3:22 PM, Neal Becker wrote:

Now what would be _really_ cool is a special array type that would represent a constant array without wasting memory.

Which again is a special case of something even cooler: lazy evaluation. This would require arrays to have immutable buffers. Then an expression like "a*x + y" would result in a symbolic representation of a * x.buffer + y.buffer Then the array could evaluate itself (it could even numexpr or a JIT compiler) when needed. The scheme would be very fragile and complicated if arrays were allowed to have immutable data buffers like those of numpy. Sturla Molden

Christopher Barker wrote:

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On 1/30/2009 3:22 PM, Neal Becker wrote:

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Now what would be _really_ cool is a special array type that would represent a constant array without wasting memory.

Can't you do that with scary stride tricks? I think I remember some discussion of this a while back.

I think that's right, but at that point, what gain is that over using a regular constant and relying on numpy's broadcasting? Ryan -- Ryan May Graduate Research Assistant School of Meteorology University of Oklahoma

On Fri, Jan 30, 2009 at 08:22, Neal Becker wrote:

Right now there are 2 options to create an array of constant value:

1) empty (size); fill (val)

2) ones (size) * val

1 has disadvantage of not being an expression, so can't be an arg to a function call.

So wrap it in a function.

Also probably slower than create+fill @ same time

Only marginally. In any case, (1) is exactly how ones() and zeros() are implemented. I would be +1 on a patch that adds a filled() function along the lines of ones() and zeros(), but I'm -1 on adding this functionality to ones() or zeros().

2 is probably slower than create+fill @ same time

Now what would be _really_ cool is a special array type that would represent a constant array without wasting memory. boost::ublas, for example, has this feature.

In [2]: from numpy.lib.stride_tricks import as_strided In [3]: def hollow_filled(shape, value, dtype=None): ...: x = asarray(value, dtype=dtype) ...: return as_strided(x, shape, [0]*len(shape)) ...: In [5]: hollow_filled([2,3,4], 5) Out[5]: array([[[5, 5, 5, 5], [5, 5, 5, 5], [5, 5, 5, 5]], [[5, 5, 5, 5], [5, 5, 5, 5], [5, 5, 5, 5]]]) In [6]: hollow_filled([2,3,4], 5.0) Out[6]: array([[[ 5., 5., 5., 5.], [ 5., 5., 5., 5.], [ 5., 5., 5., 5.]], [[ 5., 5., 5., 5.], [ 5., 5., 5., 5.], [ 5., 5., 5., 5.]]]) -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco

On Fri, Jan 30, 2009 at 16:32, Neal Becker wrote:

Robert Kern wrote:

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On Fri, Jan 30, 2009 at 08:22, Neal Becker wrote:

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Right now there are 2 options to create an array of constant value:

1) empty (size); fill (val)

2) ones (size) * val

1 has disadvantage of not being an expression, so can't be an arg to a function call.

So wrap it in a function.

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Also probably slower than create+fill @ same time

Only marginally. In any case, (1) is exactly how ones() and zeros() are implemented. I would be +1 on a patch that adds a filled() function along the lines of ones() and zeros(), but I'm -1 on adding this functionality to ones() or zeros().

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2 is probably slower than create+fill @ same time

Now what would be _really_ cool is a special array type that would represent a constant array without wasting memory. boost::ublas, for example, has this feature.

In [2]: from numpy.lib.stride_tricks import as_strided

In [3]: def hollow_filled(shape, value, dtype=None): ...: x = asarray(value, dtype=dtype) ...: return as_strided(x, shape, [0]*len(shape)) ...:

In [5]: hollow_filled([2,3,4], 5) Out[5]: array([[[5, 5, 5, 5], [5, 5, 5, 5], [5, 5, 5, 5]],

[[5, 5, 5, 5], [5, 5, 5, 5], [5, 5, 5, 5]]])

In [6]: hollow_filled([2,3,4], 5.0) Out[6]: array([[[ 5., 5., 5., 5.], [ 5., 5., 5., 5.], [ 5., 5., 5., 5.]],

[[ 5., 5., 5., 5.], [ 5., 5., 5., 5.], [ 5., 5., 5., 5.]]])

Where can I find doc on stride_tricks?

Source is always the best place. as_strided is not exposed as such since you can cause segfaults with it if you have a bug. Rather, it's useful for devs to make tools that, once debugged, can't cause segfaults.

Nothing here: http://docs.scipy.org/doc/numpy/search.html?q=stride_tricks&check_keywords=yes&area=default

Use this search box to search the development version of the docs: http://docs.scipy.org/numpy/search/ -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco

On Fri, Jan 30, 2009 at 22:16, Sturla Molden wrote:

On 1/30/2009 3:07 PM, Grissiom wrote:

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Is fill function has any advantage over ones(size)*x ?

You avoid filling with ones, all the multiplications and creating an temporary array. It can be done like this:

a = empty(size) a[:] = x

Which would be slightly faster and more memory efficient.

Hmm, I +1 on this one. It's more pythonic ;) -- Cheers, Grissiom

Sturla Molden wrote:

On 1/30/2009 2:18 PM, Neal Becker wrote:

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A nit, but it would be nice if 'ones' could fill with a value other than 1.

Maybe an optional val= keyword?

I am -1 on this. Ones should fill with ones, zeros should fill with zeros. Anything else is counter-intuitive. Calling numpy.ones to fill with fives makes no sense to me. But I would be +1 on having a function called numpy.values or numpy.fill that would create and fill an ndarray with arbitrary values.

I completely agree here. Ryan -- Ryan May Graduate Research Assistant School of Meteorology University of Oklahoma