[Python-talk] Generator Question

[Lloyd Kvam]

On Fri, 2009-08-14 at 17:19 -0400, bruce.labitt at autoliv.com wrote:
> kent3737 at gmail.com wrote on 08/13/2009 12:42:04 PM:
> 
> > On Thu, Aug 13, 2009 at 11:58 AM, <bruce.labitt at autoliv.com> wrote:
> > > Will the group of generators cascade the
> > > same?
> > 
> > Yes, all that is changing is the source of the first generator (from a
> > generator function instead of a generator expression).
> > 
> > > Say we use the previous example.  Something like this, or would I need 
> to
> > > do something different?
> > >
> > > seeds = [ <some sequence that defines the arrays to be created> ]
> > > score = 0
> > > while score < threshold:
> > >   #arrays = (make_array(seed) for seed in seeds)
> > >    arrays = make_array(seed)    # instead of line above
> > >    fft_results = (compute_fft(array) for array in arrays)
> > >    powers = (compute_power(result) for result in fft_results)
> > >    score, seeds = optimize(powers)
> > 
> > Right.
> > 
> > > This is really powerful stuff...
> > 
> > Yes :-)
> > 
> > Kent
> 
> Question about the last stage, what I would call the consumer of the 
> generator data.
> 
> I have written make_array, compute_fft, and compute_power.  Instead of 
> using the 
> routine optimize (which I have not written yet), I want to test what I 
> have.
> 
> I am trying to write a function called max_power.
> 
> The output of the function is the element by element column maximum of the 
> arrays in powers.
> 
> Consider the following as a matrix
> 

matrix = [	# added commas
> [ 0, 1, 2, 3, 4],
> [ 5, 6, 7, 8, 9],
> [10, 0, 1, 9, 7],
]	# 2 dim matrix as list of lists

> 
>  10 6 7 9 9  <== column max

# the transpose function is zip( *)
# find the max of each col
# collect the maxs with a list comprehension
In [6]: maxs = [max(col) for col in zip(*matrix)]

In [7]: maxs
Out[7]: [10, 6, 7, 9, 9]

> 
> There is a numpy function called maximum
> It returns an array c whose ith element is the maximum of (ai, bi)
> 
> c = maximum( a, b ), ci = max(ai, bi) for i in c

maxes = max(col for col
> 
> The output of max_power should be one array that is the column maximum of 
> the matrix
> 
> [ powers row 0 ] first iteration of generator
> [ powers row 1 ] 2nd
>     .
>     .
>     .
> [ powers row last ] last
> 
> 
> So I want max_power to consume all of the data from the previous stages 
> and only return
> a single row which is the column by column maximum.
> 
> Now there really isn't a real matrix here, just a series of arrays (or 
> rows) that are output
> by the previous generator.

list( generator output) will collect the outputs into a list
I presume 
	list( powers)
will create the matrix as a list of list

maxs = [ max(col) for col in zip( *list( powers)) ]

I hope that's close to what you're looking for.

> 
> I feel like I am really close here, but this conceptual part is holding me 
> back.
> 
> Any suggestions?
> 
> Thanks!
> 
> Bruce
> 
> 
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Lloyd Kvam
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