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  • what is a fast way to output h5py dataset to text?

    - by user362761
    I am using the h5py python package to read files in HDF5 format. (e.g. somefile.h5) I would like to write the contents of a dataset to a text file. For example, I would like to create a text file with the following contents: 1,20,31,75,142,324,78,12,3,90,8,21,1 I am able to access the dataset in python using this code: import h5py f = h5py.File('/Users/Me/Desktop/thefile.h5', 'r') group = f['/level1/level2/level3'] dset = group['dsetname'] My naive approach is too slow, because my dataset has over 20000 entries: # write all values to file for index in range(len(dset)): # do not add comma after last value if index == len(dset)-1: txtfile.write(repr(dset[index])) else: txtfile.write(repr(dset[index])+',') txtfile.close() return None Is there a faster way to write this to a file? Perhaps I could convert the dataset into a NumPy array or even a Python list, and then use some file-writing tool? (I could experiment with concatenating the values into a larger string before writing to file, but I'm hoping there's something entirely more elegant)

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  • Binomial test in Python for very large numbers

    - by Morlock
    I need to do a binomial test in Python that allows calculation for 'n' numbers of the order of 10000. I have implemented a quick binomial_test function using scipy.misc.comb, however, it is pretty much limited around n = 1000, I guess because it reaches the biggest representable number while computing factorials or the combinatorial itself. Here is my function: from scipy.misc import comb def binomial_test(n, k): """Calculate binomial probability """ p = comb(n, k) * 0.5**k * 0.5**(n-k) return p How could I use a native python (or numpy, scipy...) function in order to calculate that binomial probability? If possible, I need scipy 0.7.2 compatible code. Many thanks!

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  • Rapid spectral analysis of audio file using Python 2.6?

    - by Ephemeralis
    What I want to do is to have a subroutine that analyses every 200 milliseconds of a sound file which it is given and spits out the frequency intensity value (from 0 to 1 as a float) of a specific frequency range into an array which I later save. This value then goes on to be used as the opacity value for a graphic which is supposed to 'strobe' to the audio file. The problem is, I have never ventured into audio analysis before and have no clue where to start. I have looked pymedia and scipy/numpy thinking I would be able to use FFT in order to achieve this, but I am not really sure how I would manipulate this data to end up with the desired result. The documentation on the SpectrAnalyzer class of pymedia is virtually non-existant and the examples on the website do not actually work with the latest release of the library - which isn't exactly making my life easier. How would I go about starting this project? I am at a complete loss as to what libraries I should even be using.

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  • subplot matplotlib wrong syntax

    - by madptr
    I am using matplotlib to subplot in a loop. For instance, i would like to subplot 49 data sets, and from the doc, i implemented it this way; import numpy as np import matplotlib.pyplot as plt X1=list(range(0,10000,1)) X1 = [ x/float(10) for x in X1 ] nb_mix = 2 parameters = [] for i in range(49): param = [] Y = [0] * len(X1) for j in range(nb_mix): mean = 5* (1 + (np.random.rand() * 2 - 1 ) * 0.5 ) var = 10* (1 + np.random.rand() * 2 - 1 ) scale = 5* ( 1 + (np.random.rand() * 2 - 1) * 0.5 ) Y = [ Y[k] + scale * np.exp(-((X1[k] - mean)/float(var))**2) for k in range(len(X1)) ] param = param + [[mean, var, scale]] ax = plt.subplot(7, 7, i + 1) ax.plot(X1, Y) parameters = parameters + [param] ax.show() However, i have an index out of range error from i=0 onwards. Where can i do better to have it works ? Thanks

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  • what changes when your input is giga/terabyte sized?

    - by Wang
    I just took my first baby step today into real scientific computing today when I was shown a data set where the smallest file is 48000 fields by 1600 rows (haplotypes for several people, for chromosome 22). And this is considered tiny. I write Python, so I've spent the last few hours reading about HDF5, and Numpy, and PyTable, but I still feel like I'm not really grokking what a terabyte-sized data set actually means for me as a programmer. For example, someone pointed out that with larger data sets, it becomes impossible to read the whole thing into memory, not because the machine has insufficient RAM, but because the architecture has insufficient address space! It blew my mind. What other assumptions have I been relying in the classroom that just don't work with input this big? What kinds of things do I need to start doing or thinking about differently? (This doesn't have to be Python specific.)

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  • show() doesn't redraw anymore

    - by Abruzzo Forte e Gentile
    Hi All I am working in linux and I don't know why using python and matplotlib commands draws me only once the chart I want. The first time I call show() the plot is drawn, wihtout any problem, but not the second time and the following. I close the window showing the chart between the two calls. Do you know why and hot to fix it? Thanks AFG from numpy import * from pylab import * data = array( [ 1,2,3,4,5] ) plot(data) [<matplotlib.lines.Line2D object at 0x90c98ac>] show() # this call shows me a plot #..now I close the window... data = array( [ 1,2,3,4,5,6] ) plot(data) [<matplotlib.lines.Line2D object at 0x92dafec>] show() # this one doesn't shows me anything

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  • Writing to CSV issue in Spyder

    - by 0003
    I am doing the Kaggle Titanic beginner contest. I generally work in Spyder IDE, but I came across a weird issue. The expected output is supposed to be 418 rows. When I run the script from terminal the output I get is 418 rows (as expected). When I run it in Spyder IDE the output is 408 rows not 418. When I re-run it in the current python process, it outputs the expected 418 rows. I posted a redacted portion of the code that has all of the relevant bits. Any ideas? import csv import numpy as np csvFile = open("/train.csv","ra") csvFile = csv.reader(csvFile) header = csvFile.next() testFile = open("/test.csv","ra") testFile = csv.reader(testFile) testHeader = testFile.next() writeFile = open("/gendermodelDebug.csv", "wb") writeFile = csv.writer(writeFile) count = 0 for row in testFile: if row[3] == 'male': do something to row writeFile.writerow(row) count += 1 elif row[3] == 'female': do something to row writeFile.writerow(row) count += 1 else: raise ValueError("Did not find a male or female in %s" % row)

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  • Why do dicts of defaultdict(int)'s use so much memory? (and other simple python performance question

    - by dukhat
    import numpy as num from collections import defaultdict topKeys = range(16384) keys = range(8192) table = dict((k,defaultdict(int)) for k in topKeys) dat = num.zeros((16384,8192), dtype="int32") print "looping begins" #how much memory should this use? I think it shouldn't use more that a few #times the memory required to hold (16384*8192) int32's (512 mb), but #it uses 11 GB! for k in topKeys: for j in keys: dat[k,j] = table[k][j] print "done" What is going on here? Furthermore, this similar script takes eons to run compared to the first one, and also uses an absurd quantity of memory. topKeys = range(16384) keys = range(8192) table = [(j,0) for k in topKeys for j in keys] I guess python ints might be 64 bit ints, which would account for some of this, but do these relatively natural and simple constructions really produce such a massive overhead? I guess these scripts show that they do, so my question is: what exactly is causing the high memory usage in the first script and the long runtime and high memory usage of the second script and is there any way to avoid these costs?

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  • Getting PATH right for python after MacPorts install

    - by BenjaminGolder
    I can't import some python libraries (PIL, psycopg2) that I just installed with MacPorts. I looked through these forums, and tried to adjust my PATH variable in $HOME/.bash_profile in order to fix this but it did not work. I added the location of PIL and psycopg2 to PATH. I know that Terminal is a version of python in /usr/local/bin, rather than the one installed by MacPorts at /opt/local/bin. Do I need to use the MacPorts version of Python in order to ensure that PIL and psycopg2 are on sys.path when I use python in Terminal? Should I switch to the MacPorts version of Python, or will that cause more problems? In case it is helpful, here are more facts: PIl and psycopg2 are installed in /opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages which pythonreturns/usr/bin/python echo $PATHreturns (I separated each path for easy reading): :/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/ :/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages :/opt/local/bin :/opt/local/sbin :/usr/local/git/bin :/usr/bin :/bin :/usr/sbin :/sbin :/usr/local/bin :/usr/local/git/bin :/usr/X11/bin :/opt/local/bin in python, sys.path returns: /Library/Frameworks/SQLite3.framework/Versions/3/Python /Library/Python/2.6/site-packages/numpy-override /Library/Frameworks/GDAL.framework/Versions/1.7/Python/site-packages /Library/Frameworks/cairo.framework/Versions/1/Python /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python26.zip /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6 /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/plat-darwin /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/plat-mac /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/plat-mac/lib-scriptpackages /System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/lib-tk /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/lib-old /System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/lib-dynload /Library/Python/2.6/site-packages /System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/PyObjC /System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/wx-2.8-mac-unicode I welcome any criticism and comments, if any of the above looks foolish or poorly conceived. I'm new to all of this. Thanks! Running OSX 10.6.5 on a MacBook Pro, invoking python 2.6.1 from Terminal

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  • motion computation from video using pyglet in python

    - by kuaywai
    Hi, I am writing a simple motion detection program but i want it to be cross platform so im using python and the pyglet library since it provides a simple way to load videos in different formats (specially wmv and mpeg). So far i have the code given below which loads the movie and plays it in a window. Now i need to: 1) grab frame at time t and t-1 2) do a subtraction to see which pixels are active for motion detection. any ideas on how to grab frames and to skip over frames and is it possible to put the pixel values into a matrix in numpy or something directly from pyglet? or should look into using something other than pyglet? thanks kuaywai import pyglet import sys window = pyglet.window.Window(resizable=True) window.set_minimum_size(320,200) window.set_caption('Motion detect 1.0') video_intro = pyglet.resource.media('movie1.wmv') player = pyglet.media.Player() player.queue(video_intro) print 'calculating movie size...' if not player.source or not player.source.video_format: sys.exit myWidth = player.source.video_format.width myHeight = player.source.video_format.height if player.source.video_format.sample_aspect 1: myWidth *= player.source.video_format.sample_aspect elif player.source.video_format.sample_aspect < 1: myHeight /= player.source.video_format.sample_aspect print 'its size is %d,%d' % (myWidth,myHeight) player.play() @window.event def on_draw(): window.clear() (w,h) = window.get_size() player.get_texture().blit(0, h-myHeight, width=myWidth, height=myHeight) pyglet.app.run()

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  • What is the most platform- and Python-version-independent way to make a fast loop for use in Python?

    - by Statto
    I'm writing a scientific application in Python with a very processor-intensive loop at its core. I would like to optimise this as far as possible, at minimum inconvenience to end users, who will probably use it as an uncompiled collection of Python scripts, and will be using Windows, Mac, and (mainly Ubuntu) Linux. It is currently written in Python with a dash of NumPy, and I've included the code below. Is there a solution which would be reasonably fast which would not require compilation? This would seem to be the easiest way to maintain platform-independence. If using something like Pyrex, which does require compilation, is there an easy way to bundle many modules and have Python choose between them depending on detected OS and Python version? Is there an easy way to build the collection of modules without needing access to every system with every version of Python? Does one method lend itself particularly to multi-processor optimisation? (If you're interested, the loop is to calculate the magnetic field at a given point inside a crystal by adding together the contributions of a large number of nearby magnetic ions, treated as tiny bar magnets. Basically, a massive sum of these.) # calculate_dipole # ------------------------- # calculate_dipole works out the dipole field at a given point within the crystal unit cell # --- # INPUT # mu = position at which to calculate the dipole field # r_i = array of atomic positions # mom_i = corresponding array of magnetic moments # --- # OUTPUT # B = the B-field at this point def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) #4pi / mu0 (at the front of the dipole eqn) A = 1e-7 #initalise dipole field B = zeros(3,float) for i in range(len(relative)): #work out the dipole field and add it to the estimate so far B += A*(3*dot(mom_i[i],r_unit[i])*r_unit[i] - mom_i[i]) / sqrt(dot(relative[i],relative[i]))**3 return B

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  • How to compile Python scripts for use in FORTRAN?

    - by Vincent Poirier
    Hello, Although I found many answers and discussions about this question, I am unable to find a solution particular to my situation. Here it is: I have a main program written in FORTRAN. I have been given a set of python scripts that are very useful. My goal is to access these python scripts from my main FORTRAN program. Currently, I simply call the scripts from FORTRAN as such: CALL SYSTEM ('python pyexample.py') Data is read from .dat files and written to .dat files. This is how the python scripts and the main FORTRAN program communicate to each other. I am currently running my code on my local machine. I have python installed with numpy, scipy, etc. My problem: The code needs to run on a remote server. For strictly FORTRAN code, I compile the code locally and send the executable to the server where it waits in a queue. However, the server does not have python installed. The server is being used as a number crunching station between universities and industry. Installing python along with the necessary modules on the server is not an option. This means that my “CALL SYSTEM ('python pyexample.py')” strategy no longer works. Solution?: I found some information on a couple of things in thread http://stackoverflow.com/questions/138521/is-it-feasible-to-compile-python-to-machine-code Shedskin, Psyco, Cython, Pypy, Cpython API These “modules”(? Not sure if that's what to call them) seem to compile python script to C code or C++. Apparently not all python features can be translated to C. As well, some of these appear to be experimental. Is it possible to compile my python scripts with my FORTRAN code? There exists f2py which converts FORTRAN code to python, but it doesn't work the other way around. Any help would be greatly appreciated. Thank you for your time. Vincent PS: I'm using python 2.6 on Ubuntu

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  • Bibliography behaves strange in lyx.

    - by Orjanp
    Hi! I have created a Bibliography section in my document written in lyx. It uses a book layout. For some reason it did start over again when I added some more entries. The new entries was made some time later than the first ones. I just went down to key-27 and hit enter. Then it started on key-1 again. Does anyone know why it behaves like this? The lyx code is below. \begin{thebibliography}{34} \bibitem{key-6}Lego mindstorms, http://mindstorms.lego.com/en-us/default.aspx \bibitem{key-7}C.A.R. Hoare. Communicating sequential processes. Communications of the ACM, 21(8):666-677, pages 666\textendash{}677, August 1978. \bibitem{key-8}C.A.R. Hoare. Communicating sequential processes. Prentice-Hall, 1985. \bibitem{key-9}CSPBuilder, http://code.google.com/p/cspbuilder/ \bibitem{key-10}Rune Møllegård Friborg and Brian Vinter. CSPBuilder - CSP baset Scientific Workflow Modelling, 2008. \bibitem{key-11}Labview, http://www.ni.com/labview \bibitem{key-12}Robolab, http://www.lego.com/eng/education/mindstorms/home.asp?pagename=robolab \bibitem{key-13}http://code.google.com/p/pycsp/ \bibitem{key-14}Paparazzi, http://paparazzi.enac.fr \bibitem{key-15}Debian, http://www.debian.org \bibitem{key-16}Ubuntu, http://www.ubuntu.com \bibitem{key-17}GNU, http://www.gnu.org \bibitem{key-18}IVY, http://www2.tls.cena.fr/products/ivy/ \bibitem{key-19}Tkinter, http://wiki.python.org/moin/TkInter \bibitem{key-20}pyGKT, http://www.pygtk.org/ \bibitem{key-21}pyQT4, http://wiki.python.org/moin/PyQt4 \bibitem{key-22}wxWidgets, http://www.wxwidgets.org/ \bibitem{key-23}wxPython GUI toolkit, http://www.wxPython.org \bibitem{key-24}Python programming language, http://www.python.org \bibitem{key-25}wxGlade, http://wxglade.sourceforge.net/ \bibitem{key-26}http://numpy.scipy.org/ \bibitem{key-27}http://www.w3.org/XML/ \bibitem{key-1}IVY software bus, http://www2.tls.cena.fr/products/ivy/ \bibitem{key-2}sdas \bibitem{key-3}sad \bibitem{key-4}sad \bibitem{key-5}fsa \bibitem{key-6}sad \bibitem{key-7} \end{thebibliography}

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  • vtk glyphs 3D, indenpently color and rotation

    - by user3684219
    I try to display thanks to vtk (python wrapper) several glyphs in a scene with each their own colour and rotation. Unfortunately, just the rotation (using vtkTensorGlyph) is taken in consideration by vtk. Reversely, just color is taken in consideration when I use a vtkGlyph3D. Here is a ready to use piece of code with a vtkTensorGlyph. Each cube should have a random color but there all will be in the same color. I read and read again the doc of vtk but I found no solution. Thanks in advance for any idea #!/usr/bin/env python # -*- coding: utf-8 -*- import vtk import scipy.linalg as sc import random as ra import numpy as np import itertools points = vtk.vtk.vtkPoints() # where to locate each glyph in the scene tensors = vtk.vtkDoubleArray() # rotation for each glyph tensors.SetNumberOfComponents(9) colors = vtk.vtkUnsignedCharArray() # should be the color for each glyph colors.SetNumberOfComponents(3) # let's make 10 cubes in the scene for i in range(0, 50, 5): points.InsertNextPoint(i, i, i) # position of a glyph colors.InsertNextTuple3(ra.randint(0, 255), ra.randint(0, 255), ra.randint(0, 255) ) # pick random color rot = list(itertools.chain(*np.reshape(sc.orth(np.random.rand(3, 3)).transpose(), (1, 9)).tolist())) # random rotation matrix (row major) tensors.InsertNextTuple9(*rot) polydata = vtk.vtkPolyData() # create the polydatas polydata.SetPoints(points) polydata.GetPointData().SetTensors(tensors) polydata.GetPointData().SetScalars(colors) cubeSource = vtk.vtkCubeSource() cubeSource.Update() glyphTensor = vtk.vtkTensorGlyph() glyphTensor.SetColorModeToScalars() # is it really work ? try: glyphTensor.SetInput(polydata) except AttributeError: glyphTensor.SetInputData(polydata) glyphTensor.SetSourceConnection(cubeSource.GetOutputPort()) glyphTensor.ColorGlyphsOn() # should not color all cubes independently ? glyphTensor.ThreeGlyphsOff() glyphTensor.ExtractEigenvaluesOff() glyphTensor.Update() # next is usual vtk code mapper = vtk.vtkPolyDataMapper() mapper.SetInputConnection(glyphTensor.GetOutputPort()) actor = vtk.vtkActor() actor.SetMapper(mapper) ren = vtk.vtkRenderer() ren.SetBackground(0.2, 0.5, 0.3) ren.AddActor(actor) renwin = vtk.vtkRenderWindow() renwin.AddRenderer(ren) iren = vtk.vtkRenderWindowInteractor() iren.SetInteractorStyle(vtk.vtkInteractorStyleTrackballCamera()) iren.SetRenderWindow(renwin) renwin.Render() iren.Initialize() renwin.Render() iren.Start()

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  • In ParallelPython, a method of an object ( object.func() ) fails to manipulate a variable of an object ( object.value )

    - by mehmet.ali.anil
    With parallelpython, I am trying to convert my old serial code to parallel, which heavily relies on objects that have methods that change that object's variables. A stripped example in which I omit the syntax in favor of simplicity: class Network: self.adjacency_matrix = [ ... ] self.state = [ ... ] self.equilibria = [ ... ] ... def populate_equilibria(self): # this function takes every possible value that self.state can be in # runs the boolean dynamical system # and writes an integer within self.equilibria for each self.state # doesn't return anything I call this method as: Code: j1 = jobserver.submit(net2.populate_equilibria,(),(),("numpy as num")) The job is sumbitted, and I know that a long computation takes place, so I speculate that my code is ran. The problem is, i am new to parallelpython , I was expecting that, when the method is called, the variable net2.equilibria would be written accordingly, and I would get a revised object (net2) . That is how my code works, independent objects with methods that act upon the object's variables. Rather, though the computation is apparent, and reasonably timed, the variable net2.equilibria remains unchanged. As if PP only takes the function and the object, computes it elsewhere, but never returns the object, so I am left with the old one. What do I miss? Thanks in advance.

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  • Purge complete Python installation on OS X

    - by Konrad Rudolph
    I’m working on a recently-upgraded OS X Snow Leopard and MacPorts and I’m running into problems at every corner. The first problem is the sheer number of installed Python versions: altogether, there are four: 2.5, 2.6 and 3.0 in /Library/Frameworks/Python.framework 2.6 in /opt/local/Library/Frameworks/Python.framework/ (MacPorts installation) So there are at least two useless/redundant versions: 2.5 and the redundant 2.6. Additionally, the pre-installed Python is giving me severe problems because some of the pre-installed libraries (in particular, scipy, numpy and matplotlib) don’t work properly. I am sorely tempted to purge the complete /Library/Frameworks/Python.framework path, as well as the MacPorts Python installation. After that, I’ll start from a clean slate by installing a properly configured Python, e.g. that from Enthought. Am I running headlong into trouble? Or is this a sane undertaking? (In particular, I need a working Python in the next few days and if I end up with a non-working Python this would be a catastrophe of medium proportions. On the other hand, some features I need from matplotlib aren’t working now.)

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  • How to map coordinates in AxesImage to coordinates in saved image file?

    - by Vebjorn Ljosa
    I use matplotlib to display a matrix of numbers as an image, attach labels along the axes, and save the plot to a PNG file. For the purpose of creating an HTML image map, I need to know the pixel coordinates in the PNG file for a region in the image being displayed by imshow. I have found an example of how to do this with a regular plot, but when I try to do the same with imshow, the mapping is not correct. Here is my code, which saves an image and attempts to print the pixel coordinates of the center of each square on the diagonal: import numpy as np import matplotlib.pyplot as plt fig = plt.figure() ax = fig.add_axes([0.1, 0.1, 0.8, 0.8]) axim = ax.imshow(np.random.random((27,27)), interpolation='nearest') for x, y in axim.get_transform().transform(zip(range(28), range(28))): print int(x), int(fig.get_figheight() * fig.get_dpi() - y) plt.savefig('foo.png', dpi=fig.get_dpi()) Here is the resulting foo.png, shown as a screenshot in order to include the rulers: The output of the script starts and ends as follows: 73 55 92 69 111 83 130 97 149 112 … 509 382 528 396 547 410 566 424 585 439 As you see, the y-coordinates are correct, but the x-coordinates are stretched: they range from 73 to 585 instead of the expected 135 to 506, and they are spaced 19 pixels o.c. instead of the expected 14. What am I doing wrong?

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  • Handling missing/incomplete data in R--is there function to mask but not remove NAs?

    - by doug
    As you would expect from a DSL aimed at data analysis, R handles missing/incomplete data very well, for instance: Many R functions have an 'na.rm' flag that you can set to 'T' to remove the NAs: mean( c(5,6,12,87,9,NA,43,67), na.rm=T) But if you want to deal with NAs before the function call, you need to do something like this: to remove each 'NA' from a vector: vx = vx[!is.na(a)] to remove each 'NA' from a vector and replace it w/ a '0': ifelse(is.na(vx), 0, vx) to remove entire each row that contains 'NA' from a data frame: dfx = dfx[complete.cases(dfx),] All of these functions permanently remove 'NA' or rows with an 'NA' in them. Sometimes this isn't quite what you want though--making an 'NA'-excised copy of the data frame might be necessary for the next step in the workflow but in subsequent steps you often want those rows back (e.g., to calculate a column-wise statistic for a column that has missing rows caused by a prior call to 'complete cases' yet that column has no 'NA' values in it). to be as clear as possible about what i'm looking for: python/numpy has a class, 'masked array', with a 'mask' method, which lets you conceal--but not remove--NAs during a function call. Is there an analogous function in R?

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  • Would anybody recommend learning J/K/APL?

    - by ozan
    I came across J/K/APL a few months ago while working my way through some project euler problems, and was intrigued, to say the least. For every elegant-looking 20 line python solution I produced, there'd be a gobsmacking 20 character J solution that ran in a tenth of the time. I've been keen to learn some basic J, and have made a few attempts at picking up the vocabulary, but have found the learning curve to be quite steep. To those who are familiar with these languages, would you recommend investing some time to learn one (I'm thinking J in particular)? I would do so more for the purpose of satisfying my curiosity than for career advancement or some such thing. Some personal circumstances to consider, if you care to: I love mathematics, and use it daily in my work (as a mathematician for a startup) but to be honest I don't really feel limited by the tools that I use (like python + NumPy) so I can't use that excuse. I have no particular desire to work in the finance industry, which seems to be the main port of call for K users at least. Plus I should really learn C# as a next language as it's the primary language where I work. So practically speaking, J almost definitely shouldn't be the next language I learn. I'm reasonably familiar with MATLAB so using an array-based programming language wouldn't constitute a tremendous paradigm shift. Any advice from those familiar with these languages would be much appreciated.

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  • Building a ctypes-"based" C library with distutils

    - by Robie Basak
    Following this recommendation, I have written a native C extension library to optimise part of a Python module via ctypes. I chose ctypes over writing a CPython-native library because it was quicker and easier (just a few functions with all tight loops inside). I've now hit a snag. If I want my work to be easily installable using distutils using python setup.py install, then distutils needs to be able to build my shared library and install it (presumably into /usr/lib/myproject). However, this not a Python extension module, and so as far as I can tell, distutils cannot do this. I've found a few references to people other people with this problem: Someone on numpy-discussion with a hack back in 2006. Somebody asking on distutils-sig and not getting an answer. Somebody asking on the main python list and being pointed to the innards of an existing project. I am aware that I can do something native and not use distutils for the shared library, or indeed use my distribution's packaging system. My concern is that this will limit usability as not everyone will be able to install it easily. So my question is: what is the current best way of distributing a shared library with distutils that will be used by ctypes but otherwise is OS-native and not a Python extension module? Feel free to answer with one of the hacks linked to above if you can expand on it and justify why that is the best way. If there is nothing better, at least all the information will be in one place.

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  • Python on Mac: Fink? MacPorts? Builtin? Homebrew? Binary installer?

    - by BastiBechtold
    For the last few days, I have been trying to use Python for some audio development. The thing is, Mac OSX does not handle uninstalling stuff well. Actually, there is no way to uninstall anything. Once it is on your system, you better pray that it didn't do any funny stuff. Hence, I don't really want to rely on installer packages for Python. So I turn to Homebrew and install Python using Homebrew. Works fabulously. Using pip, Numpy, SciPy, Matplotlib were no (big) problem, either. Now I want to play audio. There is a host of different packages out there, but pip does not seem willing to install any. But, there is a binary distribution for PyGame, which I guess should work with the built-in Python. Hence my question: What would you do? Would you just install the binary distributions and hope that they interoperate well and never need uninstalling? Would you hack your way through whichever package control management system you prefer and deal with its problems? Something else?

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  • Python: Serial Transmission

    - by Silent Elektron
    I have an image stack of 500 images (jpeg) of 640x480. I intend to make 500 pixels (1st pixels of all images) as a list and then send that via COM1 to FPGA where I do my further processing. I have a couple of questions here: How do I import all the 500 images at a time into python and how do i store it? How do I send the 500 pixel list via COM1 to FPGA? I tried the following: Converted the jpeg image to intensity values (each pixel is denoted by a number between 0 and 255) in MATLAB, saved the intensity values in a text file, read that file using readlines(). But it became too cumbersome to make the intensity value files for all the 500 images! Used NumPy to put the read files in a matrix and then pick the first pixel of all images. But when I send it, its coming like: [56, 61, 78, ... ,71, 91]. Is there a way to eliminate the [ ] and , while sending the data serially? Thanks in Advance! :)

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  • Statistical analysis on large data set to be published on the web

    - by dassouki
    I have a non-computer related data logger, that collects data from the field. This data is stored as text files, and I manually lump the files together and organize them. The current format is through a csv file per year per logger. Each file is around 4,000,000 lines x 7 loggers x 5 years = a lot of data. some of the data is organized as bins item_type, item_class, item_dimension_class, and other data is more unique, such as item_weight, item_color, date_collected, and so on ... Currently, I do statistical analysis on the data using a python/numpy/matplotlib program I wrote. It works fine, but the problem is, I'm the only one who can use it, since it and the data live on my computer. I'd like to publish the data on the web using a postgres db; however, I need to find or implement a statistical tool that'll take a large postgres table, and return statistical results within an adequate time frame. I'm not familiar with python for the web; however, I'm proficient with PHP on the web side, and python on the offline side. users should be allowed to create their own histograms, data analysis. For example, a user can search for all items that are blue shipped between week x and week y, while another user can search for sort the weight distribution of all items by hour for all year long. I was thinking of creating and indexing my own statistical tools, or automate the process somehow to emulate most queries. This seemed inefficient. I'm looking forward to hearing your ideas Thanks

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  • Modify passed, nested dict/list

    - by Gerenuk
    I was thinking of writing a function to normalize some data. A simple approach is def normalize(l, aggregate=sum, norm_by=operator.truediv): aggregated=aggregate(l) for i in range(len(l)): l[i]=norm_by(l[i], aggregated) l=[1,2,3,4] normalize(l) l -> [0.1, 0.2, 0.3, 0.4] However for nested lists and dicts where I want to normalize over an inner index this doesnt work. I mean I'd like to get l=[[1,100],[2,100],[3,100],[4,100]] normalize(l, ?? ) l -> [[0.1,100],[0.2,100],[0.3,100],[0.4,100]] Any ideas how I could implement such a normalize function? Maybe it would be crazy cool to write normalize(l[...][0]) Is it possible to make this work?? Or any other ideas? Also not only lists but also dict could be nested. Hmm... EDIT: I just found out that numpy offers such a syntax (for lists however). Anyone know how I would implement the ellipsis trick myself?

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  • Length-1 arrays can be converted to python scalars error? python

    - by Randy
    from numpy import * from pylab import * from math import * def LogisticMap(a,x): return 4.*a*x*(1.-x) def CosineMap(a,x): return a*cos(x/(2.*pi)) def TentMap(a,x): if x>= 0 or x<0.5: return 2.*a*x if x>=0.5 or x<=1.: return 2.*a*(1.-x) a = 0.98 N = 40 xaxis = arange(0.0,N,1.0) Func = CosineMap subplot(211) title(str(Func.func_name) + ' at a=%g and its second iterate' %a) ylabel('X(n+1)') # set y-axis label plot(xaxis,Func(a,xaxis), 'g', antialiased=True) subplot(212) ylabel('X(n+1)') # set y-axis label xlabel('X(n)') # set x-axis label plot(xaxis,Func(a,Func(a,xaxis)), 'bo', antialiased=True) My program is supposed to take any of the three defined functions and plot it. They all take in a value x from the array xaxis from 0 to N and then return the value. I want it to plot a graph of xaxis vs f(xaxis) with f being any of the three above functions. The logisticmap function works fine, but for CosineMap i get the error "only length-1 arrays can be converted to python scalars" and for TentMap i get error "The truth value of an array with more than one element is ambiguous, use a.any() or a.all()". My tent map function is suppose to return 2*a*x if 0<=x<0.5 and it's suppose to return 2*a*(1-x) if 0.5<=0<=1.

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