Mailman 3 March 2011 - NumPy-Discussion

moving window product
by Brent Pedersen March 21, 2011

March 21, 2011

hi, is there a way to take the product along a 1-d array in a moving window? -- similar to convolve, with product in place of sum? currently, i'm column_stacking the array with offsets of itself into window_size columns and then taking the product at axis 1. like:: w = np.column_stack(a[i:-window_size+i] for i in range(0, window_size)) window_product = np.product(w, axis=1) but then there are the edge effects/array size issues--like those handled in np.convolve. it there something in numpy/scipy that addresses this. or that does the column_stacking with an offset? thanks, -brent

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convert dictionary of arrays into single array
by John March 21, 2011

March 21, 2011

Hello, I have a dictionary with structured arrays, keyed by integers 0...n. There are no other keys in the dictionary. What is the most efficient way to convert the dictionary of arrays to a single array? All the arrays have the same 'headings' and width, but different lengths. Is there something I can do that would be more efficient than looping through and using np.concatenate (vstack)? --john

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Re: [Numpy-discussion] What Requires C and what is just python
by Hans-Martin v. Gaudecker March 21, 2011

March 21, 2011

>>>> So, in addition to my computer science work, I'm a PhD student in econ. Right now, the class is using GAUSS for almost everything. This sort of pisses me off because it means people are building libraries of code that become valueless when they graduate (because right now we get GAUSS licenses for free, but it is absurdly expensive later) -- particularly when this is the only language they know. That's precisely the reason we just switched our PhD computational econometrics course from GAUSS to NumPy/SciPy/statsmodels/matplotlib :-) Although some of my colleagues are not completely convinced yet... > this looks interesting on this topic: > > http://www.vwl.uni-mannheim.de/gaudecker/teaching.htm > > Josef Well, the only closely related thing there are the 'installation instructions', other than that it's really an adaption of http://software-carpentry.org/ for economists. >>>> So, I had this idea of building some command line tools to do the same things using the most basic pieces of NumPy (arrays, dot products, transpose and inverse -- that's it). And it is going great. My problem however is that I'd like to be able to share these tools but I know I'm opening up a big can of worms where I have to go around building numpy on 75 peoples computers. I don't think that will be an issue -- most of my students (in either the course Josef linked to above or the econometrics one) had not used anything else than Stata or Matlab before, let alone installed something on their own. Nobody reported any problems when following the above-mentioned guide. The installers work great now, only thing missing currently is a matplotlib installer on 64-bit MacOS. My 2 cents. Cheers, Hans-Martin

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What Requires C and what is just python
by Ben Smith March 21, 2011

March 21, 2011

So, in addition to my computer science work, I'm a PhD student in econ. Right now, the class is using GAUSS for almost everything. This sort of pisses me off because it means people are building libraries of code that become valueless when they graduate (because right now we get GAUSS licenses for free, but it is absurdly expensive later) -- particularly when this is the only language they know. So, I had this idea of building some command line tools to do the same things using the most basic pieces of NumPy (arrays, dot products, transpose and inverse -- that's it). And it is going great. My problem however is that I'd like to be able to share these tools but I know I'm opening up a big can of worms where I have to go around building numpy on 75 peoples computers. What I'd like to do is limit myself to just the functions that are implemented in python, package it with py2exe and hand that to anyone that needs it. So, my question, if anyone knows, what's implemented in python and what depends on the c libraries? Is this even possible? Thanks! Ben -- Ben Smith Founder / CSA WBP SYSTEMS http://www.wbpsystems.com

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1.6: branching and release notes
by Ralf Gommers March 21, 2011

March 21, 2011

Hi all, On Tuesday (~2am GMT) I plan to create the 1.6.x branch and tag the first beta. So please get your last commits for 1.6 in by Monday evening. Also, please review and add to the 1.6.0 release notes. I put in headers for several items that need a few lines in the notes, I hope this can be filled in by the authors of those features (Charles: Legendre polynomials, Pearu: assumed shape arrays, Mark: a bunch of stuff). Cheers, Ralf

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Re: [Numpy-discussion] Cellular Automata Neighborhoods & Numpy
by Robert Cimrman March 20, 2011

March 20, 2011

Hi Michael, You can find the full game of life script at [1]. There is also Belousov-Zhabotinsky cellular automaton. Both have a strided version. r. [1] http://docs.sfepy.org/scientific-python-tutorial/examples ----- Reply message ----- From: "Michael Mersky" <me(a)mydis.org> To: <numpy-discussion(a)scipy.org> Subject: [Numpy-discussion] Cellular Automata Neighborhoods & Numpy Date: Sun, Mar 20, 2011 03:35 Hello, I stumbled upon this group tonight (http://mail.scipy.org/pipermail/numpy-discussion/2010-October/053420.html) while searching Google for examples of Cellular Automata(CA) using Numpy. The "Game of Life Strides" example looks great, but I don't fully comprehend how this example is working: http://scipy.org/Cookbook/GameOfLifeStrides If I have: >>> world=arange(9).reshape(3,3) >>> world array([[0, 1, 2], [3, 4, 5], [6, 7, 8]]) how could I as_strided(world,shape?,strides) such that my 9 cell neighborhood at [0][0] would be something like this (i.e. wrapped): array([[8,6,7], [2,0,1], [5,3,4]]) Greatly appreciate your help! -m

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Cellular Automata Neighborhoods & Numpy
by Michael Mersky March 20, 2011

March 20, 2011

Hello, I stumbled upon this group tonight ( http://mail.scipy.org/pipermail/numpy-discussion/2010-October/053420.html) while searching Google for examples of Cellular Automata(CA) using Numpy. The "Game of Life Strides" example looks great, but I don't fully comprehend how this example is working: http://scipy.org/Cookbook/GameOfLifeStrides If I have: >>> world=arange(9).reshape(3,3) >>> world array([[0, 1, 2], [3, 4, 5], [6, 7, 8]]) how could I as_strided(world,shape?,strides) such that my 9 cell neighborhood at [0][0] would be something like this (i.e. wrapped): array([[8,6,7], [2,0,1], [5,3,4]]) Greatly appreciate your help! -m

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BUG: ndarray subclass calls __mul__ when ** (pow) is involved
by Dmitrey March 19, 2011

March 19, 2011

I have ndarray subclass, its instance x and use r = x**2 I expected it will call for each array element elem.__pow__(2) but it calls elem.__mul__(elem) instead. It essentially (tens or even more times) decreases my calculations speed for lots of cases. >>> numpy.__version__ '2.0.0.dev-1fe8136' (taken some days ago from git) doesn't work with 1.3.0 as well..

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Extracting data from genfromtxt?
by Rohaq March 19, 2011

March 19, 2011

I've got a CSV file with the following layout: Location,Result1,Result2 1,0,0 2,0,0 3,1,0 4,1,0 5,1,1 6,0,1 7,0,1 8,0,0 ...etc., and I've loaded it using the following: import numpy as np data = np.genfromtxt('file.csv',delimiter=',',dtype=None,names=True) Resulting in the following: array([(1, 0, 0), (2, 0, 0), (3, 0, 0), ..., (16382, 0, 0), (16383, 0, 0), (16384, 0, 0)], dtype=[('Location', '<i8'), ('Result1', '<i8'), ('Result2', '<i8')]) I want to plot the data in matplotlib.pyplot, but I'm having trouble reshaping the data into something it'll recognise. I can pull the Location easily enough with data['Location'], but I need to get the results from every other column present. There could be a lot more than 2 other columns, Result3,Result4, etc., so I need to code it to be scalable; if this were acting like a normal dict, I could write a loop that iterates over the keys, and loads the results data into a new object, but I can't seem to find a function that will return the keys so that I can do this. Can anybody offer any tips for this? I'm fairly new to Python/Numpy, so any help is appreciated. Cheers, Rohaq

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split() for slices?
by Benjamin Root March 18, 2011

March 18, 2011

Hello, I really like the split() family of functions, but I have the need to split multiple arrays in a similar manner, and it would seem logical to me to have a split() function that would return a list of slice tuples that I could use on multiple arrays. Is there such a function? Thanks, Ben Root

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