Velocity Reviews > numpy - 2D matrix/array - initialization like in Matlab...

# numpy - 2D matrix/array - initialization like in Matlab...

someone
Guest
Posts: n/a

 10-15-2012

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!

MRAB
Guest
Posts: n/a

 10-15-2012
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]])

Emile van Sebille
Guest
Posts: n/a

 10-15-2012
someone wrote:
> 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!

You could use string interpolation:

Dx = numpy.matrix('%s %s %s; %s %s -0.5; 0 -0.5 1.5'
% (test11 test12 test13 test21 test22))

Emile

someone
Guest
Posts: n/a

 10-15-2012
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.

Marco Nawijn
Guest
Posts: n/a

 10-16-2012
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

Marco Nawijn
Guest
Posts: n/a

 10-16-2012
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