Mailman 3 August 2007 - NumPy-Discussion

fromfunction question
by john saponara 08 Aug '07

08 Aug '07

Thinking I could use fromfunction to generate the x,y,z coordinates of a 3D surface, I instead got separate arrays of x, y, and z coordinates (as I should have expected) and needed to use a nested listcomp to produce the unified array of 3D points: x,y,z=fromfunction( lambda i,j: (xfun(i,j),yfun(i,j),zfun(i,j)), (1,3), dtype=int ) result=[[(a,b,c) for a,b,c in zip(p,q,r)] for p,q,r in zip(x,y,z)] Is it possible to compute the unified array of 3-tuples in a single step? Below is working code. Thanks. --- start python session --- r=array([[0,1],[1,0],[2,1]]) c=array([[0,1],[1,0],[2,1]]) p=array([[-1,0]]) rLen=len(r) cLen=len(c) # functions to compute x,y,z coordinates of 3d points (the exact expressions are not important) def xfun(i,j): return r[j,0] def yfun(i,j): return r[j,1]*p[i,0]+c[i+1,0] def zfun(i,j): return r[j,1]*p[i,1]+c[i+1,1] # the fromfunction and an extra step to arrange coordinates into 3-tuples x,y,z=fromfunction( lambda i,j: (xfun(i,j),yfun(i,j),zfun(i,j)), (1,3), dtype=int ) result=[[(a,b,c) for a,b,c in zip(p,q,r)] for p,q,r in zip(x,y,z)] print result # prints [[(0, 0, 0), (1, 1, 0), (2, 0, 0)]] --- end python session ---

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vectorized function inside a class
by mark 08 Aug '07

08 Aug '07

I am trying to figure out a way to define a vectorized function inside a class. This is what I tried: class test: def __init__(self): self.x = 3.0 def func(self,y): rv = self.x if y > self.x: rv = y return rv f = vectorize(func) >>> m = test() >>> m.f( m, [-20,4,6] ) array([ 3., 4., 6.]) But as you can see, I can only call the m.f function when I also pass it the instance m again. I really want to call it as m.f( [-20,4,6] ) But then I get an error ValueError: mismatch between python function inputs and received arguments Any ideas how to do this better? Mark

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Count the occurrence of a certain integer in a list of integers
by Mark.Miller 08 Aug '07

08 Aug '07

A late entry, but here's something that gets you an array of counts for each unique integer: >>> data = numpy.array([9, 6, 9, 6, 7, 9, 9, 10, 7, 9, 9, 6, 7, 9, 8, 8, 11, 9, 6, 7, 10, 9, 7, 9, 7, 8, 9, 8, 7, 9]) >>> unique=numpy.unique(data) >>> unique array([ 6, 7, 8, 9, 10, 11]) >>> histo=numpy.histogram(data,unique) >>> histo (array([ 4, 7, 4, 12, 2, 1]), array([ 6, 7, 8, 9, 10, 11])) >>> So histo[0] includes the counts of each integer in data. -Mark 2007/8/7, Nils Wagner <nwagner(a)iam.uni-stuttgart.de>: > > Hi all, > > I have a list of integer numbers. The entries can vary between 0 and 19. > How can I count the occurrence of any number. Consider > > >>> data > [9, 6, 9, 6, 7, 9, 9, 10, 7, 9, 9, 6, 7, 9, 8, 8, 11, 9, 6, 7, 10, 9, 7, > 9, 7, 8, 9, 8, 7, 9] > > > Is there a better way than using, e.g. > > >>> shape(where(array(data)==10))[1] > 2 > > > to compute the occurrence of 10 in the list which is 2 in this case ? > > Nils

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simple slicing question
by mark 08 Aug '07

08 Aug '07

Consider the array d: d = linspace( -10, 10, 10 ) If I want to multiply every value above -5 by 100 I can do d[ d>-5 ] *= 100 But what if I want to multiply every value between -5 and +5 by 100. This does NOT work: d[ d>-5 and d<5 ] *= 100 Any ideas? Thanks, Mark

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numpy installation problem
by kingshuk ghosh 08 Aug '07

08 Aug '07

Hi, I downloaded numpy1.0.3-2.tar and unzipped and untared. However somehow new numpy does not work. It invokes the old numpy 0.9.6 when i import numpy from python and type in numpy.version.version . I tried to change path and once I do that and when I do import numpy it says "running from source directory" and then if I try numpy.version.version it gives some error. Is there something obvious I am missing after unzipping and untaring the numpy source file ? For example do I need to do something to install the new numpy1.0.3 ? Or do I also need to download full python package ? I am trying to run this on Red Hat Linux 3.2.2-5 which has a gcc 3.2.2 and the version of python is 2.4 . Any help will be greatly appreciated. Cheers Kings

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ANN: PyQwt3D-0.1.6 released
by Gerard Vermeulen 07 Aug '07

07 Aug '07

What is PyQwt3D ( http://pyqwt3d.sourceforge.net) ? - it is a set of Python bindings for the QwtPlot3D C++ class library which extends the Qt framework with widgets for 3D data visualization. PyQwt3D inherits the snappy feel from QwtPlot3D. The examples at http://pyqwt.sourceforge.net/pyqwt3d-examples.html show how easy it is to make a 3D plot and how to save a 3D plot to an image or an (E)PS/PDF/PGF/SVG file. - it requires and extends PyQt, a set of Python bindings for Qt. - it supports the use of PyQt, Qt, QwtPlot3D, and NumPy or SciPy in a GUI Python application or in an interactive Python session. - it runs on POSIX, Mac OS X and Windows platforms (practically any platform supported by Qt and Python). - it is licensed under the GPL with an exception to allow dynamic linking with non-free releases of Qt and PyQt. The home page of PyQwt3D is http://pyqwt.sourceforge.net. PyQwt3D-0.1.6 is a bug fix release: - Improved text display on screen and in pixmaps with Qt-4 and X (requires the use of the patched QwtPlot3D-0.2.7 library included in PyQwt3D). PyQwt3D-0.1.6 supports: 1. Python-2.5, or -2.4. 2. PyQt-4.3, -4.2, -4.1, or -3.17. 3. SIP-4.7, -4.6, or -4.5. 4. Qt-4.3, -4.2, Qt-3.3, or -3.2. 5. QwtPlot3D-0.2.7. Enjoy -- Gerard Vermeulen

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spurious IndexError?
by john saponara 07 Aug '07

07 Aug '07

Using numpy-1.0.2/python-2.5/winxp pro sp2: in the following, the only array is 'a', and I'm not using it as an index, so why do I get the IndexError below? --- start python session --- >>> a=array([[1,3],[2,4]]) >>> a array([[1, 3], [2, 4]]) >>> f=lambda i,j: a[i,j] >>> f(1,1) 4 >>> fromfunction(f,(2,2)) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python25\Lib\site-packages\numpy\core\numeric.py", line 514, in fromfunction return function(*args,**kwargs) File "<stdin>", line 1, in <lambda> IndexError: arrays used as indices must be of integer (or boolean) type --- end python session --- The upstream maple is written in 'fromfunction' style, and I have no control over that but want to port it to python in the most natural way possible. The session suggests that lambda has no trouble with an array, so the problem seems to be related to the way 'fromfunction' works. What am I missing? Thanks!

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Count the occurrence of a certain integer in a list of integers
by Nils Wagner 07 Aug '07

07 Aug '07

Hi all, I have a list of integer numbers. The entries can vary between 0 and 19. How can I count the occurrence of any number. Consider >>> data [9, 6, 9, 6, 7, 9, 9, 10, 7, 9, 9, 6, 7, 9, 8, 8, 11, 9, 6, 7, 10, 9, 7, 9, 7, 8, 9, 8, 7, 9] Is there a better way than using, e.g. >>> shape(where(array(data)==10))[1] 2 to compute the occurrence of 10 in the list which is 2 in this case ? Nils

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Re: [Numpy-discussion] fourier with single precision
by Lars Friedrich 07 Aug '07

07 Aug '07

Thank you for your comments! I will try this fftw3-scipy approach and see how much faster I can get. Maybe this is enough for me...? Lars

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ANN: PyQwt3D-0.1.5 released
by Gerard Vermeulen 07 Aug '07

07 Aug '07

What is PyQwt3D ( http://pyqwt3d.sourceforge.net) ? - it is a set of Python bindings for the QwtPlot3D C++ class library which extends the Qt framework with widgets for 3D data visualization. PyQwt3D inherits the snappy feel from QwtPlot3D. The examples at http://pyqwt.sourceforge.net/pyqwt3d-examples.html show how easy it is to make a 3D plot and how to save a 3D plot to an image or an (E)PS/PDF/PGF/SVG file. - it requires and extends PyQt, a set of Python bindings for Qt. - it supports the use of PyQt, Qt, QwtPlot3D, and NumPy or SciPy in a GUI Python application or in an interactive Python session. - it runs on POSIX, Mac OS X and Windows platforms (practically any platform supported by Qt and Python). The home page of PyQwt3D is http://pyqwt.sourceforge.net. New features and bugfixes in PyQwt3D-0.1.5: - Added support for QwtPlot3D-0.2.7 - Added support for SIP-4.7, PyQt-4.3 and PyQt-3.17.3. - Added support for SVG and PGF vector output. - Added Qwt3D.save() to facilitate saving plots to a file. - Added Qwt3D.plot() to facilitate function plotting with nicely scaled axes. - Fixed the type of the result of IO.outputHandler(format). - Fixed saving to pixmap formats in qt4examples/Grab.py. PyQwt3D-0.1.5 supports: 1. Python-2.5, or -2.4. 2. PyQt-4.3, -4.2, -4.1, or -3.17. 3. SIP-4.7, -4.6, or -4.5. 4. Qt-4.3, -4.2, Qt-3.3, or -3.2. 5. QwtPlot3D-0.2.7. Enjoy -- Gerard Vermeulen

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