[Numpy-discussion] The problem with arrays

[Fabrice Silva]

Le mardi 22 septembre 2009 à 23:00 +0530, yogesh karpate a écrit :

> This is the main thing . When I try to store it in array like
> R_time=array([R_t[0][i]]). It just stores the final value in that
> array when loop ends.I cant get out of this For loop.I really have
> this small problem. I really need help on this guys.
> 
>         for i in range(a1):
>                 data_temp=(bpf[left[0][i]:
>         right[0][i]])# left is an array and right is also an array
>                 maxloc=data_temp.argmax()       #taking indices of
>         max. value of data segment
>                 maxval=data_temp[maxloc]         
>                 minloc=data_temp.argmin()
>                 minval=data_temp[minloc]
>                 maxloc = maxloc-1+left # add offset of present
>         location
>                 minloc = minloc-1+left # add offset of present
>         location
>                 R_index = maxloc
>                 R_t = t[maxloc]
>                 R_amp = array([maxval])
>                 S_amp = minval#%%% Assuming the S-wave is the lowest
>                 #%%% amp in the given window
>                 #S_t = t[minloc]
>                 R_time=array([R_t[0][i]])
>                 plt.plot(R_time,R_amp,'go');
>                 plt.show()

Two options :
- you define an empty list before the loop
        >>> R_time = []
  and you append the computed value while looping
        >>> for i:
        >>>	...
        >>>	R_time.append(t[maxloc])

- or you define a preallocated array before the loop
        >>> R_time = np.empty(a1)
  and fill it with the computed values
        >>> for i:
        >>>	...
        >>>	R_time[i] = t[maxloc]


Same thing with R_amp. After looping, whatever the solution you choose,
you can plot  the whole set of (time, value) tuples
        >>> plt.plot(R_time, R_amp)

-- 
Fabrice Silva <silva@lma.cnrs-mrs.fr>
LMA UPR CNRS 7051