Mailman 3 January 2016 - NumPy-Discussion

mixed mode arithmetic
by Neal Becker 11 Jul '23

11 Jul '23

I've been browsing the numpy source. I'm wondering about mixed-mode arithmetic on arrays. I believe the way numpy handles this is that it never does mixed arithmetic, but instead converts arrays to a common type. Arguably, that might be efficient for a mix of say, double and float. Maybe not. But for a mix of complex and a scalar type (say, CDouble * Double), it's clearly suboptimal in efficiency. So, do I understand this correctly? If so, is that something we should improve?

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Invalid value encoutered : how to prevent numpy.where to do this?
by Eric Emsellem 18 Feb '23

18 Feb '23

Dear all, I have a code using lots of "numpy.where" to make some constrained calculations as in: data = arange(10) result = np.where(data == 0, 0., 1./data) # or data1 = arange(10) data2 = arange(10)+1.0 result = np.where(data1 > data2, np.sqrt(data1-data2), np.sqrt(data2-data2)) which then produces warnings like: /usr/bin/ipython:1: RuntimeWarning: invalid value encountered in sqrt or for the first example: /usr/bin/ipython:1: RuntimeWarning: divide by zero encountered in divide How do I avoid these messages to appear? I know that I could in principle use numpy.seterr. However, I do NOT want to remove these warnings for other potential divide/multiply/sqrt etc errors. Only when I am using a "where", to in fact avoid such warnings! Note that the warnings only happen once, but since I am going to release that code, I would like to avoid the user to get such messages which are irrelevant here (because I am testing, with the where, when NOT to divide by zero or take a sqrt of a negative number). thanks! Eric

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Re: [Numpy-discussion] example reading binary Fortran file
by Neil Martinsen-Burrell 22 Jul '21

22 Jul '21

David Froger <david.froger.info <at> gmail.com> writes: > Hy,My question is about reading Fortran binary file (oh no this question > again...) I've posted this before, but I finally got it cleaned up for the Cookbook. For this purpose I use a subclass of file that has methods for reading unformatted Fortran data. See http://www.scipy.org/Cookbook/FortranIO/FortranFile. I'd gladly see this in numpy or scipy somewhere, but I'm not sure where it belongs. > program makeArray > implicit none > integer,parameter:: nx=10,ny=20 > real(4),dimension(nx,ny):: ux,uy,p > integer :: i,j > open(11,file='uxuyp.bin',form='unformatted') > do i = 1,nx > do j = 1,ny > ux(i,j) = real(i*j) > uy(i,j) = real(i)/real(j) > p (i,j) = real(i) + real(j) > enddo > enddo > write(11) ux,uy > write(11) p > close(11) > end program makeArray When I run the above program compiled with gfortran on my Intel Mac, I can read it back with:: >>> import numpy as np >>> from fortranfile import FortranFile >>> f=FortranFile('uxuyp.bin', endian='<') >>> uxuy = f.readReals(prec='f') # 'f' for default reals >>> len(uxuy) 400 >>> ux = np.array(uxuy[:200]).reshape((20,10)).T >>> uy = np.array(uxuy[200:]).reshape((20,10)).T >>> p = f.readReals('f').reshape((20,10)).T >>> ux array([[ 1., 2., 3., 4., 5., 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20.], [ 2., 4., 6., 8., 10., 12., 14., 16., 18., 20., 22., 24., 26., 28., 30., 32., 34., 36., 38., 40.], [ 3., 6., 9., 12., 15., 18., 21., 24., 27., 30., 33., 36., 39., 42., 45., 48., 51., 54., 57., 60.], [ 4., 8., 12., 16., 20., 24., 28., 32., 36., 40., 44., 48., 52., 56., 60., 64., 68., 72., 76., 80.], [ 5., 10., 15., 20., 25., 30., 35., 40., 45., 50., 55., 60., 65., 70., 75., 80., 85., 90., 95., 100.], [ 6., 12., 18., 24., 30., 36., 42., 48., 54., 60., 66., 72., 78., 84., 90., 96., 102., 108., 114., 120.], [ 7.,Proxy-Connection: keep-alive Cache-Control: max-age=0 14., 21., 28., 35., 42., 49., 56., 63., 70., 77., 84., 91., 98., 105., 112., 119., 126., 133., 140.], [ 8., 16., 24., 32., 40., 48., 56., 64., 72., 80., 88., 96., 104., 112., 120., 128., 136., 144., 152., 160.], [ 9., 18., 27., 36., 45., 54., 63., 72., 81., 90., 99., 108., 117., 126., 135., 144., 153., 162., 171., 180.], [ 10., 20., 30., 40., 50., 60., 70., 80., 90., 100., 110., 120., 130., 140., 150., 160., 170., 180., 190., 200.]]) >>> uy array([[ 1. , 0.5 , 0.33333334, 0.25 , 0.2 , 0.16666667, 0.14285715, 0.125 , 0.11111111, 0.1 , 0.09090909, 0.08333334, 0.07692308, 0.07142857, 0.06666667, 0.0625 , 0.05882353, 0.05555556, 0.05263158, 0.05 ], [ 2. , 1. , 0.66666669, 0.5 , 0.40000001, 0.33333334, 0.2857143 , 0.25 , 0.22222222, 0.2 , 0.18181819, 0.16666667, 0.15384616, 0.14285715, 0.13333334, 0.125 , 0.11764706, 0.11111111, 0.10526316, 0.1 ], [ 3. , 1.5 , 1. , 0.75 , 0.60000002, 0.5 , 0.42857143, 0.375 , 0.33333334, 0.30000001, 0.27272728, 0.25 , 0.23076923, 0.21428572, 0.2 , 0.1875 , 0.17647059, 0.16666667, 0.15789473, 0.15000001], [ 4. , 2. , 1.33333337, 1. , 0.80000001, 0.66666669, 0.5714286 , 0.5 , 0.44444445, 0.40000001, 0.36363637, 0.33333334, 0.30769232, 0.2857143 , 0.26666668, 0.25 , 0.23529412, 0.22222222, 0.21052632, 0.2 ], [ 5. , 2.5 , 1.66666663, 1.25 , 1. , 0.83333331, 0.71428573, 0.625 , 0.55555558, 0.5 , 0.45454547, 0.41666666, 0.38461539, 0.35714287, 0.33333334, 0.3125 , 0.29411766, 0.27777779, 0.2631579 , 0.25 ], [ 6. , 3. , 2. , 1.5 , 1.20000005, 1. , 0.85714287, 0.75 , 0.66666669, 0.60000002, 0.54545456, 0.5 , 0.46153846, 0.42857143, 0.40000001, 0.375 , 0.35294119, 0.33333334, 0.31578946, 0.30000001], [ 7. , 3.5 , 2.33333325, 1.75 , 1.39999998, 1.16666663, 1. , 0.875 , 0.77777779, 0.69999999, 0.63636363, 0.58333331, 0.53846157, 0.5 , 0.46666667, 0.4375 , 0.41176471, 0.3888889 , 0.36842105, 0.34999999], [ 8. , 4. , 2.66666675, 2. , 1.60000002, 1.33333337, 1.14285719, 1. , 0.8888889 , 0.80000001, 0.72727275, 0.66666669, 0.61538464, 0.5714286 , 0.53333336, 0.5 , 0.47058824, 0.44444445, 0.42105263, 0.40000001], [ 9. , 4.5 , 3. , 2.25 , 1.79999995, 1.5 , 1.28571427, 1.125 , 1. , 0.89999998, 0.81818181, 0.75 , 0.69230771, 0.64285713, 0.60000002, 0.5625 , 0.52941179, 0.5 , 0.47368422, 0.44999999], [ 10. , 5. , 3.33333325, 2.5 , 2. , 1.66666663, 1.42857146, 1.25 , 1.11111116, 1. , 0.90909094, 0.83333331, 0.76923078, 0.71428573, 0.66666669, 0.625 , 0.58823532, 0.55555558, 0.52631581, 0.5 ]]) >>> p array([[ 2., 3., 4., 5., 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21.], [ 3., 4., 5., 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22.], [ 4., 5., 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23.], [ 5., 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24.], [ 6., 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25.], [ 7., 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25., 26.], [ 8., 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25., 26., 27.], [ 9., 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25., 26., 27., 28.], [ 10., 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25., 26., 27., 28., 29.], [ 11., 12., 13., 14., 15., 16., 17., 18., 19., 20., 21., 22., 23., 24., 25., 26., 27., 28., 29., 30.]]) Note that you have to provide the shape information for ux and uy because fortran writes them together as a stream of 400 numbers. -Neil

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C-API: multidimensional array indexing?
by Johann Bauer 31 Mar '16

31 Mar '16

Dear experts, is there a C-API function for numpy which implements Python's multidimensional indexing? Say, I have a 2d-array PyArrayObject * M; and an index int i; how do I extract the i-th row or column M[i,:] respectively M[:,i]? I am looking for a function which gives again a PyArrayObject * and which is a view to M (no copied data; the result should be another PyArrayObject whose data and strides points to the correct memory portion of M). I searched the API documentation, Google and mailing lists for quite a long time but didn't find anything. Can you help me? Thanks, Johann

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FeatureRequest: support for array construction from iterators
by Stephan Sahm 18 Feb '16

18 Feb '16

[ this request /discussion refers to numpy issue #5863 https://github.com/numpy/numpy/pull/5863#issuecomment-159738368 ] Dear all, As far as I can think, the expected functionality of np.array(...) would be np.array(list(...)) or something even nicer. Therefore, I like to request a generator/iterator support for np.array(...) as far as list(...) supports it. A more detailed reasoning behind this follows now. In general it seems possible to identify iterators/generators as needed for this purpose: - someone actually implemented this feature already (see #5863 <https://mail.google.com/mail/u/0/%E2%80%8Bhttps://github.com/numpy/numpy/pu…> ) - there is ``type.GeneratorType`` and ``collections.abc.Iterator`` for ``isinstance(...)`` check - numpy can destinguish them already from all other types which get well translated into a numpy array Given this, I think the general argument goes roughly like the following: PROS (effect maybe 10% of numpy user or more): - more intuitive overall behaviour, array(...) = array(list(...)) roughly - python3 compatibility (see e.g. #5951 <https://github.com/numpy/numpy/issues/5951>) - compatibility with analog ``__builtin__`` functions (see e.g. #5756 <https://github.com/numpy/numpy/issues/5756>) - all the above make numpy easier to use in an interactive style (e.g. ipython --pylab) (computation not that important, however coding time well) CONS (effect less than 0.1% numpy user I would guess): - might break existing code which in total, at least for me at this stage, speaks in favour of merging the already existing featurebranch (see #5863 <https://mail.google.com/mail/u/0/%E2%80%8Bhttps://github.com/numpy/numpy/pu…> ) or something similar into numpy master . Discussion, please! cheers, Stephan

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Numpy 1.11.0b2 released
by Charles R Harris 10 Feb '16

10 Feb '16

Hi All, I hope I am pleased to announce the Numpy 1.11.0b2 release. The first beta was a damp squib due to missing files in the released source files, this release fixes that. The new source filese may be downloaded from sourceforge, no binaries will be released until the mingw tool chain problems are sorted. Please test and report any problem. Chuck

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Numpy 1.11.0b1 is out
by Charles R Harris 01 Feb '16

01 Feb '16

Hi All, I'm pleased to announce that Numpy 1.11.0b1 <http://sourceforge.net/projects/numpy/files/NumPy/1.11.0b1/> is now available on sourceforge. This is a source release as the mingw32 toolchain is broken. Please test it out and report any errors that you discover. Hopefully we can do better with 1.11.0 than we did with 1.10.0 ;) Chuck

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Numpy pull requests getting out of hand.
by Charles R Harris 01 Feb '16

01 Feb '16

Hi All, There are now 130 open numpy pull requests and it seems almost impossible to keep that number down. My personal decision is that I am going to ignore any new enhancements for the next couple of months and only merge bug fixes, tests, house keeping (style, docs, deprecations), and old PRs. I would also request that other maintainers start looking a taking care of older PRs, either cleaning them up and merging, or closing them. Chuck

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Problem with NumPy 1.10.4 with ATLAS on Python 2.7.8
by Davide Vanzo 28 Jan '16

28 Jan '16

Hi all, I recently upgraded NumPy from 1.9.1 to 1.10.4 on Python 2.7.8 by using pip. As always I specified the paths to Blas, Lapack and Atlas in the respective environment variables. I used the same compiler I used to compile both Python and the libraries (GCC 4.6.1). The problem is that it always tries to get Blas symbols in the wrong library: >>> import numpy Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/python2/2.7.8/x86_64/gcc46/New_build/lib/python2.7/site- packages/numpy/__init__.py", line 180, in <module> from . import add_newdocs File "/usr/local/python2/2.7.8/x86_64/gcc46/New_build/lib/python2.7/site- packages/numpy/add_newdocs.py", line 13, in <module> from numpy.lib import add_newdoc File "/usr/local/python2/2.7.8/x86_64/gcc46/New_build/lib/python2.7/site- packages/numpy/lib/__init__.py", line 8, in <module> from .type_check import * File "/usr/local/python2/2.7.8/x86_64/gcc46/New_build/lib/python2.7/site- packages/numpy/lib/type_check.py", line 11, in <module> import numpy.core.numeric as _nx File "/usr/local/python2/2.7.8/x86_64/gcc46/New_build/lib/python2.7/site- packages/numpy/core/__init__.py", line 14, in <module> from . import multiarray ImportError: /usr/local/python2/2.7.8/x86_64/gcc46/New_build/lib/python2.7/site- packages/numpy/core/multiarray.so: undefined symbol: cblas_sgemm I also tried to install from source instead of pip but no luck either. The only way to get it to work is to downgrade to 1.9.1. Any idea why? Thanks. Davide

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Proposal for IQR function
by Joseph Fox-Rabinovitz 28 Jan '16

28 Jan '16

I have created an IQR function to add to the other dispersion metrics such as standard deviation. I have described the purpose and nature of the proposal in PR#7137, so I am pasting the text here as well: Motivation ---------- This function is used in one place in numpy already (to compute the Freedman-Diaconis histogram bin estimator) in addition to being requested on Stack Overflow a couple of times: - http://stackoverflow.com/questions/23228244/how-do-you-find-the-iqr-in-numpy - http://stackoverflow.com/questions/27472330/how-should-the-interquartile-ra… It is also used in matplotlib for box and violin plots: http://matplotlib.org/faq/howto_faq.html#interpreting-box-plots-and-violin-…. It is a very simple, common and robust dispersion estimator. There does not appear to be an implementation for it anywhere in numpy or scipy. About --------- This function is a convenience combination of `np.percentile` and `np.subtract`. As such, it allows the the difference between any two percentiles to be computed, not necessarily (25, 75), which is the default. All of the recent enhancements to percentile are used. The documentation and testing is borrowed heavily from `np.percentile`. Wikipedia Reference: https://en.wikipedia.org/wiki/Interquartile_range Note ---------- The tests will not pass until the bug-fix for `np.percentile` kwarg `interpolation='midpoint'` (#7129) is incorporated and this PR is rebased.

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