Re: [Numpy-discussion] Array accumulation in numpy

[Eraldo Pomponi]

Dear Tony,

I would suggest to look at this post already mentioned by Benjamin .
maybe it fits with your needs!
http://numpy-discussion.10968.n7.nabble.com/Pre-allocate-array-td4870.html

Cheers,
Eraldo



On Tue, Feb 19, 2013 at 4:24 PM, Tony Ladd  wrote:

> Thanks to all for a very quick response. np.bincount does what I need.
>
> Tony
>
> On 02/19/2013 10:04 AM, Benjamin Root wrote:
> >
> >
> > On Tue, Feb 19, 2013 at 10:00 AM, Tony Ladd  > > wrote:
> >
> > I want to accumulate elements of a vector (x) to an array (f) based
> on
> > an index list (ind).
> >
> > For example:
> >
> > x=[1,2,3,4,5,6]
> > ind=[1,3,9,3,4,1]
> > f=np.zeros(10)
> >
> > What I want would be produced by the loop
> >
> > for i=range(6):
> >  f[ind[i]]=f[ind[i]]+x[i]
> >
> > The answer is f=array([ 0.,  7.,  0.,  6.,  5.,  0.,  0.,  0.,
> >  0., 3.])
> >
> > When I try to use implicit arguments
> >
> > f[ind]=f[ind]+x
> >
> > I get f=array([ 0.,  6.,  0.,  4.,  5.,  0.,  0.,  0.,  0.,  3.])
> >
> >
> > So it takes the last value of x that is pointed to by ind and adds
> > it to
> > f, but its the wrong answer when there are repeats of the same
> > entry in
> > ind (e.g. 3 or 1)
> >
> > I realize my code is incorrect, but is there a way to make numpy
> > accumulate without using loops? I would have thought so but I cannot
> > find anything in the documentation.
> >
> > Would much appreciate any help - probably a really simple question.
> >
> > Thanks
> >
> > Tony
> >
> >
> > I believe you are looking for the equivalent of accumarray in Matlab?
> >
> > Try this:
> >
> > http://www.scipy.org/Cookbook/AccumarrayLike
> >
> > It is a bit touchy about lists and 1-D numpy arrays, but it does the job.
> > Also, I think somebody posted an optimized version for simple sums
> > recently to this list.
> >
> > Cheers!
> > Ben Root
> >
> >
> >
> > ___
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> > http://mail.scipy.org/mailman/listinfo/numpy-discussion
>
> --
> Tony Ladd
>
> Chemical Engineering Department
> University of Florida
> Gainesville, Florida 32611-6005
> USA
>
> Email: tladd-"(AT)"-che.ufl.edu
> Webhttp://ladd.che.ufl.edu
>
> Tel:   (352)-392-6509
> FAX:   (352)-392-9514
>
>
>
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Re: [Numpy-discussion] numpy.mean problems

[Eraldo Pomponi]

Hi Fred,

I would suggest you to have a look at pandas (http://pandas.sourceforge.net/)
. It was
really helpful for me. It seems well suited for the type of data that you
are working
with. It has nice "brodcasting" capabilities to apply numpy functions to a
set column.
http://pandas.sourceforge.net/basics.html#descriptive-statistics
http://pandas.sourceforge.net/basics.html#function-application

Cheers,
Eraldo


On Sun, Dec 11, 2011 at 1:49 PM, ferreirafm wrote:

>
>
> Aronne Merrelli wrote:
> >
> > I can recreate this error if tab is a structured ndarray - what is the
> > dtype of tab?
> >
> > If that is correct, I think you could fix this by simplifying things.
> > Since
> > tab is already an ndarray, you should not need to convert it back into a
> > python list. By converting the ndarray back to a list you are making an
> > extra level of "wrapping" as a python object, which is ultimately why you
> > get that error about adding numpy.void.
> >
> > Unfortunately you cannot take directly take a mean of a struct dtype;
> > structs are generic so they could have fields with strings, or objects,
> > etc, that would be invalid for a mean calculation. However the following
> > code fragment should work pretty efficiently. It will make a 1-element
> > array of the same dtype as tab, and then populate it with the mean value
> > of
> > all elements where the length is >= 15. Note that dtype.fields.keys()
> > gives
> > you a nice way to iterate over the fields in the struct dtype:
> >
> > length_mask = tab['length'] >= 15
> > tab_means = np.zeros(1, dtype=tab.dtype)
> > for k in tab.dtype.fields.keys():
> > tab_means[k] = np.mean( tab[k][mask] )
> >
> > In general this would not work if tab has a field that is not a simple
> > numeric type, such as a str, object, ... But it looks like your arrays
> are
> > all numeric from your example above.
> >
> > Hope that helps,
> > Aronne
> >
> HI Aronne,
> Thanks for your replay. Indeed, tab is a mix of different column types:
> tab.dtype:
> [('sgi', ' ('positive', ' ' ' '  Interestingly, I couldn't be able to import some columns of digits as
> strings like as with R dataframe objects.
> I'll try to adapt your example to my needs and let you know the results.
> Regards.
>
> --
> View this message in context:
> http://old.nabble.com/numpy.mean-problems-tp32945124p32955052.html
> Sent from the Numpy-discussion mailing list archive at Nabble.com.
>
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Re: [Numpy-discussion] numpy.mean problems

[Eraldo Pomponi]

Hi Fred,

Pandas has a nice interface to PyTable if you still need it:

http://pandas.sourceforge.net/io.html#hdf5-pytables

However, my intention was just to point you to pandas because it
is really a powerful tool if you need to deal with tabular heterogenic
data. It is also important to notice that there are plans in the numpy
community to include/port "part" of this package directly in the codebase.
This says a lot about how good it is...

Best,
Eraldo

On Tue, Dec 13, 2011 at 9:01 PM, ferreirafm wrote:

>
> Hi Eraldo,
> Thanks for your suggestion. I was using pytables but give up after known
> that some very useful capabilities are sold as a professional package.
> However, it still useful to many printing and data manipulation and, also,
> it can handle extremely large datasets (which is not my case.).
> Regards,
> Fred
>
>
> Eraldo Pomponi wrote:
> >
> > I would suggest you to have a look at pandas
> > (http://pandas.sourceforge.net/)
> > . It was
> > really helpful for me. It seems well suited for the type of data that you
> > are working
> > with. It has nice "brodcasting" capabilities to apply numpy functions to
> a
> > set column.
> > http://pandas.sourceforge.net/basics.html#descriptive-statistics
> > http://pandas.sourceforge.net/basics.html#function-application
> >
> > Cheers,
> > Eraldo
> >
>
> --
> View this message in context:
> http://old.nabble.com/numpy.mean-problems-tp32945124p32970295.html
> Sent from the Numpy-discussion mailing list archive at Nabble.com.
>
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Re: [Numpy-discussion] scipy installation problem

[Eraldo Pomponi]

Dear Alexe,

I'm not sure I understood what you mean by "install" like Ralf.
However, I would also suggest, if you are using Eclipse and PyDev, (after
installing new modules) to remove the current python interpreter (from
Eclipse options) and then re-add it so that the whole pythonpath will be
re-scanned and you will not see any  "red"  underline (with the msg: module
not found) in your python editor.

Cheers,
Eraldo


On Wed, Dec 14, 2011 at 10:52 PM, Ralf Gommers
wrote:

>
>
> On Wed, Dec 14, 2011 at 10:38 PM, Alex Ter-Sarkissov 
> wrote:
>
>> I'm using Eclipse (PyDev) on MacOS. I downloaded scipy010, installed it
>> and added path to .mpkg file to PYTHONPATH and scipy to forced built-in.
>> Nothing worked, I keep getting 'module scipy not found'. I then removed the
>> link to the .mpkg and still nothing works. Strange enough, numpy works just
>> fine. What should I do?
>>
>>
> Not sure what you mean by "install" here, but you're supposed to
> double-click the mpkg installer to run it, not put it on your PYTHONPATH.
> Note that to use the provided dmg installer, you have to also use the
> matching python from python.org
>
> Ralf
>
>
>
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Re: [Numpy-discussion] getting the equivalent complex dtype from a real or int array

[Eraldo Pomponi]

> We really ought to have a special page for all of Robert's little gems!
>

I'm totally in favor or having that page. In my gmail account almost every
Robert's answer gets a star!!!
Maybe one day I'll try to put them together.

Cheers,
EP
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Re: [Numpy-discussion] 100 Numpy exercices

[Eraldo Pomponi]

>
> It doesn't use stride_tricks, and seberg doesn't quite like it, but this
> made the rounds in StackOverflow a couple of years ago:
>
>
> http://stackoverflow.com/questions/16970982/find-unique-rows-in-numpy-array/16973510#16973510
>
> It may not work properly on floats, but I think it is a very cool use of
> dtypes. Then again I'm obviously biased...
>

I remained astonished when I discovered this trick just the day before
Nicolas posted about his amazing contribution  and for my use case (int
matrices) it is working perfectly ...
another candy, again from you Jaime is the fast moving average in:

http://stackoverflow.com/a/14314054

but at a much lower ranking respect to the previous one :P .

Let me thank you all a lot for making the life of mine and many others
easier
sharing your knowledge.

Cheers,
Eraldo
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Re: [Numpy-discussion] IDE's for numpy development?

[Eraldo Pomponi]

Sorry for the OT and top-posting but,

It reminds me of "ITex" (https://www.youtube.com/watch?v=eKaI78K_rgA) ...

On Wed, Apr 1, 2015 at 6:43 PM, Yuxiang Wang  wrote:

> That would really be hilarious - and "IFortran" probably! :)
>
> Shawn
>
> On Wed, Apr 1, 2015 at 12:07 PM, Benjamin Root  wrote:
> > mixed C and python development? I would just wait for the Jupyter folks
> to
> > create "IC" and maybe even "IC++"!
> >
> > On Wed, Apr 1, 2015 at 12:04 PM, Charles R Harris
> >  wrote:
> >>
> >> Hi All,
> >>
> >> In a recent exchange Mark Wiebe suggested that the lack of support for
> >> numpy development in Visual Studio might limit the number of developers
> >> attracted to the project. I'm a vim/console developer myself and make no
> >> claim of familiarity with modern development tools, but I wonder if such
> >> tools might now be available for Numpy. A quick google search turns up a
> >> beta plugin for Visual Studio,, and there is an xcode IDE for the mac
> that
> >> apparently offers some Python support. The two things that I think are
> >> required are: 1) support for mixed C, python developement and 2)
> support for
> >> building and testing numpy. I'd be interested in information from anyone
> >> with experience in using such an IDE and ideas of how Numpy might make
> using
> >> some of the common IDEs easier.
> >>
> >> Thoughts?
> >>
> >> Chuck
> >>
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> >
> >
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>
>
>
> --
> Yuxiang "Shawn" Wang
> Gerling Research Lab
> University of Virginia
> yw...@virginia.edu
> +1 (434) 284-0836
> https://sites.google.com/a/virginia.edu/yw5aj/
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