Mailman 3 May 2006 - NumPy-Discussion

masked arrays
by John Hunter 31 May '06

31 May '06

I'm a bit of an ma newbie. I have a 2D masked array R and want to extract the non-masked values in the last column. Below I use logical indexing, but I suspect there is a "built-in" way w/ masked arrays. I read through the docstring, but didn't see anything better. In [66]: c = R[:,-1] In [67]: m = R.mask[:,-1] In [69]: c[m==0] Out[69]: array(data = [ 0.94202899 0.51839465 0.24080268 0.26198439 0.29877369 2.06856187 0.91415831 0.64994426 0.96544036 1.11259755 2.53623188 0.71571906 0.18394649 0.78037904 0.60869565 3.56744705 0.44147157 0.07692308 0.27090301 0.16610925 0.57068004 0.80267559 0.57636566 0.23634337 1.9509476 0.50761427 0.09587514 0.45039019 0.14381271 0.69007804 2.44481605 0.2909699 0.45930881 1.37123746 2.00668896 3.1638796 1.0735786 1.06800446 0.18952062 1.55964326 1.16833891 0.17502787 1.16610925 0.85507246 0.42140468 0.04236343 1.01337793 0.22853958 1.76365663 1.78372352 0.96209588 0.73578595 0.94760312 1.59531773 0.88963211], mask = [False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False False], fill_value=1e+20)

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Distutils problem with g95
by James Graham 31 May '06

31 May '06

numpy.distutils seems to have difficulties detecting the current version of the g95 compiler. I believe this is because the output of `g95 --version` has changed. The patch below seems to correct the problem (i.e. it now works with the latest g95) but my regexp foo is very weak so it may not be correct/optimal. --- /usr/lib64/python2.3/site-packages/numpy/distutils/fcompiler/g95.py 2006-01-06 21:29:40.000000000 +0000 +++ /home/jgraham/lib64/python/numpy/distutils/fcompiler/g95.py 2006-05-26 12:49:50.000000000 +0100 @@ -9,7 +9,7 @@ class G95FCompiler(FCompiler): compiler_type = 'g95' - version_pattern = r'G95.*\(experimental\) \(g95!\) (?P<version>.*)\).*' + version_pattern = r'G95.*(?:\(experimental\))? \(g95!\) (?P<version>.*)\).*' executables = { 'version_cmd' : ["g95", "--version"], -- "You see stars that clear have been dead for years But the idea just lives on..." -- Bright Eyes

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Re: Any Numeric or numarray users on this list?
by RayS 31 May '06

31 May '06

At 08:10 PM 5/30/2006, you wrote: >1) Have you transitioned or started to transition to NumPy (i.e. import >numpy)? only by following the threads here, so far no download yet >2) Will you transition within the next 6 months? (if you answered No to #1) yes, on this next project (assuming the small array, <2048, performance compares to Numeric >3) Please, explain your reason(s) for not making the switch. (if you >answered No to #2) if no, it is because most projects involve small bin number FFTs and correlations >4) Please provide any suggestions for improving NumPy. 24 bit signed integer type, for the new class of ADCs coming out (or at least the ability to cast efficiently to Float32) a GPU back-end option for FFT ;-) Thanks, it's all good, Ray

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when does numpy create temporaries ?
by Simon Burton 31 May '06

31 May '06

Consider these two operations: >>> a=numpy.empty( 1024 ) >>> b=numpy.empty( 1024 ) >>> a[1:] = b[:-1] >>> a[1:] = a[:-1] >>> It seems that in the second operation we need to copy the view a[:-1] but in the first operation we don't need to copy b[:-1]. How does numpy detect this, or does it always copy the source when assigning to a slice ? I've poked around the (numpy) code a bit and tried some benchmarks, but it's still not so clear to me. Simon. -- Simon Burton, B.Sc. Licensed PO Box 8066 ANU Canberra 2601 Australia Ph. 61 02 6249 6940 http://arrowtheory.com

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arrays that start from negative numbers?
by Rick Muller 30 May '06

30 May '06

Is it possible to create arrays that run from, say -5:5, rather than 0:11? Analogous to the Fortran "allocate(A(-5:5))" command? I'm translating a F90 code to Python, and it would be easier to do this than to use a python dictionary. Thanks in advance. Rick Muller rmuller(a)sandia.gov

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Re: 24bit arrays
by Ray Schumacher 30 May '06

30 May '06

>Is there some clever way to achieve the same goal for 24bit data without >copying everything into a new 32-bit array? I agree with the other post, Int8 x 3 can be used with slices to get a lot done, depending on data tasks desired, but not all >The typical 24bit audio file contains two interleaved channels, i.e. >frames of 3bytes+3bytes, so it can be cast to (nframes,3) Int32, or >(nframes,2,3) Int8 array, but this is hardly a useful representation for >audio data. Along these liners, I have been working with 24 bit ADC data returned from pyUSB as tuples, which I need to convert to Float32 and save, like this: WRAP = 2.**23 BITS24 = 2.**24 try: chValue = struct.unpack(">I", struct.pack(">4b", 0,*dataTuple[byteN:byteN+3]) )[0] except: chValue = 0 if chValue>WRAP: chValue = ((BITS24-chValue) / WRAP) * gainFactors[thisCh] else: chValue = (-chValue / WRAP) * gainFactors[thisCh] data[thisCh].append(chValue) which is really slow (no real time is possible). Is there a much faster way evident to others here? We are going to do a pyd in C otherwise... Ray

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{Info} st ock speculation for
by rxctaeg olwhljm 30 May '06

30 May '06

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...never mind, found everything
by Paul Dubois 29 May '06

29 May '06

Please disregard my previous posting about my special issue correspondence. All is well. Gmail and my twitching don't work well together. I need a computer that ignores me.

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Special issue of CiSE on Python -- Correspondents please reply
by Paul Dubois 29 May '06

29 May '06

In April I sent out a request for proposals for a special issue of Computing in Science and Engineering on Python's use in science and engineering. Due to being somewhat inexperienced with a new mailer, I lost some of the correspondence. Would those with whom I corresponded send me back something about what we were talking about? I know some additional people had gotten dragged into the conversation. I did not lose letters from: Jarrod Millman Kent-Andre Mardal Xuan Shi Ryan Krauss I have the word doc only from Peter Bienstman. I have the text outline only from Arnd Baecker Sorry to be so clumsy. Paul Dubois

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24bit arrays
by Maxim Krikun 29 May '06

29 May '06

Hi all. I'm writing a tool to access uncompressed audio files (currently in wave, aiff and wave64 formats) using numarray.memmap module -- it maps the whole file to memory, then finds the waveform data region and casts it to and array of appropriate type and shape. This works pretty well for both 16-bit integer and 32-bit float data, but not for 24-bit files, since there is no Int24 data type in numarray. Is there some clever way to achieve the same goal for 24bit data without copying everything into a new 32-bit array? The typical 24bit audio file contains two interleaved channels, i.e. frames of 3bytes+3bytes, so it can be cast to (nframes,3) Int32, or (nframes,2,3) Int8 array, but this is hardly a useful representation for audio data. --Maxim

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