On Tuesday, October 16, 2012 12:43:09 AM UTC+2, someone wrote:
> On 10/15/2012 11:26 PM, MRAB wrote:
>
> > On 2012-10-15 22:09, someone wrote:
>
> >>
>
> >> See this:
>
> >>
>
> >> ==========================================================
>
> >> In [5]: Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 1.5')
>
> >>
>
> >> In [6]: Dx
>
> >> Out[6]:
>
> >> matrix([[ 1. , 0. , 0. ],
>
> >> [ 0. , 0.5, -0.5],
>
> >> [ 0. , -0.5, 1.5]])
>
> >> ==========================================================
>
> >>
>
> >>
>
> >>
>
> >> Ok... So now test = 33 and instead of the value 1.5 I want to use the
>
> >> value of "test" and put it directly into the matrix (or array):
>
> >>
>
> >> ==========================================================
>
> >> In [7]: test=33
>
> >>
>
> >> In [8]: Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 test')
>
> >> ---------------------------------------------------------------------------
>
> >>
>
> >> NameError Traceback (most recent call
>
> >> last)
>
> >> /home/user/something/<ipython-input-8-5a43575649e1> in <module>()
>
> >> ----> 1 Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 test')
>
> >>
>
> >> /usr/lib/python2.7/dist-packages/numpy/matrixlib/defmatrix.pyc in
>
> >> __new__(subtype, data, dtype, copy)
>
> >> 252
>
> >> 253 if isinstance(data, str):
>
> >> --> 254 data = _convert_from_string(data)
>
> >> 255
>
> >> 256 # now convert data to an array
>
> >> ...... etc...
>
> >> ==========================================================
>
> >>
>
> >>
>
> >>
>
> >> So obviously it doesn't understand that I want this:
>
> >>
>
> >> ==========================================================
>
> >> In [21]: Dx[2,2]=test
>
> >>
>
> >> In [22]: Dx
>
> >> Out[22]:
>
> >> matrix([[ 1. , 0. , 0. ],
>
> >> [ 0. , 33. , -0.5],
>
> >> [ 0. , -0.5, 33. ]])
>
> >> ==========================================================
>
> >>
>
> >> Without having to manually change all the individual places using my
>
> >> variables (test is actually many variables, not just one but I think you
>
> >> should understand the problem now).
>
> >>
>
> >>
>
> >> How to initialize my array directly using variables ?
>
> >>
>
> >> It could also be that I wanted:
>
> >>
>
> >> test11 = 1
>
> >> test12 = 1.5
>
> >> test13 = 2
>
> >> test21 = 0
>
> >> test22 = 5
>
> >>
>
> >> Dx = numpy.matrix('test11 test12 test13; test21 test22 -0.5; 0 -0.5 1.5')
>
> >>
>
> >> Etc... for many variables...
>
> >>
>
> >> Appreciate ANY help, thank you very much!
>
> >>
>
> > What it prints should give you a hint:
>
> >
>
> > >>> Dx = numpy.matrix([[test11, test12, test13], [test21, test22,
>
> > -0.5], [0, -0.5, 1.5]])
>
> > >>> Dx
>
> > matrix([[ 1. , 1.5, 2. ],
>
> > [ 0. , 5. , -0.5],
>
> > [ 0. , -0.5, 1.5]])
>
>
>
> Uh, great - thank you very much!
>
>
>
> As you maybe see, I'm only a python newbie so I'm not so good at
>
> understanding the error messages and reading the source code yet.
>
>
>
> Thank you very much for the solution to the problem! It's highly
>
> appreciated. Thanks.
Hi,
Also note that you don't need to initialize the array with a string. You could
directly do it like this:
>>> a = numpy.array(((1,2,3), (2,3,4), (4,5,6)))
Other things that might be interesting for you are:
# List comprehension (standard python) to convert strings to floats
>>> vals = [ float(s) for s in "1.0 2.3 1.2".split() ]
produces [1.0, 2.3, 1.2]
>>> vals = [ float(s) for s in ("1.0", "2.3", "1.2") ]
produces again [1.0, 2.3, 1.2]
Also lookup the documentation for numpy.reshape. With this you could provide a
single list of for example 9 numbers and reshape it into a 3x3 array.
Python and Numpy are so cool!!
Marco
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