[Tutor] Appending an extra column in a data file

[Sayan Chatterjee]

Yup it's exactly what I want!

I want *many* data files,not one...to make an animation out of it. For a
data file t is constant.

the solution you have just mentioned i.e np.array([t,pp_za,pv_za]) is
giving the following error:


Traceback (most recent call last):
  File "ZA_Phase_Plot.py", line 38, in <module>
    np.savetxt(fname, np.array([pp_za,pv_za,t]).T, '%f')
  File "/usr/lib/python2.7/dist-packages/numpy/lib/npyio.py", line 979, in
savetxt
    fh.write(asbytes(format % tuple(row) + newline))
TypeError: float argument required, not numpy.ndarray

What to do? :-|

Sayan



On 10 April 2013 23:17, Andre' Walker-Loud <walksloud at gmail.com> wrote:

> Hi Sayan,
>
> > Well,this is the concerned snippet of the code:
> >
> >
> > while t < 1:
> >
> >
> >   pp_za = pp_init + t*K*np.sin(K*pp_init)
> >
> > # Periodic Boundary Condition
> >
> >   for i in range(0,999):
> >
> >     if pp_za[i] < 0:
> >       pp_za[i] = 2 - abs(pp_za[i])
> >     if pp_za[i] > 2:
> >       pp_za[i] = pp_za[i] % 2
> >
> >   pv_za = +K*np.sin(K*pp_init)
> >
> >   fname = 'file_' + str(t) + '.dat'
> >
> > # Generating dataset for Phase Space diagram
> >
> >   np.savetxt(fname, np.array([pp_za,pv_za]).T, '%f')
> >
> >   t = t + 0.01
>
> To answer your question, to add "t" to the array, you can simply replace
> the current np.array command with either of the following
>
> np.array([pp_za,pv_za,t])
>
> or
>
> np.array([t,pp_za,pv_za])
>
> depending if you want "t" is the first element of the data or the last.
> Also, you are "transposing" the array with the ".T", so this will write
> the data in sequential lines, rather than a single line (row) with multiple
> entries.  I just bring it up because it is not the "obvious" way to pack
> the data.
>
> Also, it looks like you are generating a separate file for each "t".
> Is this what you want?
> I assume you want a single data file that stores this info, not many data
> files.
>
>
> Andre
>
>
>
>
>
> >
> > And the sample data generated is :
> >
> > 0.105728 0.098678
> > 0.126865 0.118406
> > 0.147998 0.138128
> > 0.169126 0.157845
> > 0.190247 0.177556
> > 0.211362 0.197259
> > 0.232469 0.216955
> > 0.253567 0.236643
> > 0.274657 0.256321
> > 0.295737 0.275989
> > 0.316806 0.295646
> >
> > Precisely what I want is, I want to add the 't' (over which the while
> loop is run) in the 3 rd column. 't' is float and constant for each
> looping. If you know what a phase plot is(doesn't matter if you don't), I
> want to see the phase plot evolving with time. Thus the need of a time axis
> and hence plot with V(velocity-Yaxis), X ( Position -X axis) and t (Time-Z
> axis).
> >
> > I hope your first example might help.Though,I think,I need some tweaking
> to fit to my needs.
> >
> > Regards,
> > Sayan
> >
> >
> > On 10 April 2013 22:38, Andre' Walker-Loud <walksloud at gmail.com> wrote:
> > Hi Sayan,
> >
> > > Thank Andre for your prompt answer.
> >
> > No problem.
> >
> > > I'll figure out the plotting issue once the dat files are made. So
> it's the primary concern.
> > > For an example I am attaching a dat file herewith. The two columns
> here are 2 numpy arrays.I want to add a third column, to be precise, I want
> to print a parameter value on the third column of the file.
> >
> > Let me try again.
> > The reason the matplotlib list would be a better place is this is a
> general python list, and most people are not familiar with numpy.  However,
> most people who use matplotlib are familiar with numpy.
> >
> > I am hoping you can describe precisely the structure of the data.  Maybe
> show a little code on how it is created, or how you access it.  I am not
> keen to open "random" files from the internet.  As two examples of how I
> think your code might be packed
> >
> > 1/
> > '''
> > x = numpy.zeros([10]) # 1D numpy array of dimension 10
> > y = numpy.zeros([10]) # 1D numpy array of dimension 10
> > your_data = []
> > your_data.append(x)
> > your_data.append(y)
> > '''
> >
> > so now your data is a table with two entries, and each entry is a numpy
> array.
> > You have in mind adding a third entry to the table with just floats.
> >
> > 2/
> > '''
> > your_data = numpy.zeros([10,10]) # initialize a 2D numpy array with all
> zeros
> > for i in range(your_data.shape[0]):
> >     for j in range(your_data.shape[1]):
> >         your_data[i,j] = data[i][j] # I am assuming the data is imported
> already and called data and is in a python list/table format
> > '''
> >
> > Now you want to make a new column or row for your data file, which
> contains floats.  Well, all the entries inside the numpy array are already
> floats, so it is not clear to me why you want a new column that is not a
> numpy array. So it would be nice if you could precisely describe what you
> currently have and what you want.
> >
> >
> > Hope this helps,
> >
> > Andre
> >
> >
> >
> >
> >
> > --
> >
> >
> >
> --------------------------------------------------------------------------
> > Sayan  Chatterjee
> > Dept. of Physics and Meteorology
> > IIT Kharagpur
> > Lal Bahadur Shastry Hall of Residence
> > Room AB 205
> > Mob: +91 9874513565
> > blog: www.blissprofound.blogspot.com
> >
> > Volunteer , Padakshep
> > www.padakshep.org
>
>


-- 


--------------------------------------------------------------------------
*Sayan  Chatterjee*
Dept. of Physics and Meteorology
IIT Kharagpur
Lal Bahadur Shastry Hall of Residence
Room AB 205
Mob: +91 9874513565
blog: www.blissprofound.blogspot.com

Volunteer , Padakshep
www.padakshep.org
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