[Numpy-discussion] puzzle: generate index with many ranges

Jim Vickroy Jim.Vickroy@noaa....
Fri Jan 30 12:37:41 CST 2009


Raik Gruenberg wrote:
> Jim Vickroy wrote:
>   
>> Raik Gruenberg wrote:
>>     
>>> Hi there,
>>>
>>> perhaps someone has a bright idea for this one:
>>>
>>> I want to concatenate ranges of numbers into a single array (for indexing). So I
>>> have generated an array "a" with starting positions, for example:
>>>
>>> a = [4, 0, 11]
>>>
>>> I have an array b with stop positions:
>>>
>>> b = [11, 4, 15]
>>>
>>> and I would like to generate an index array that takes 4..11, then 0..4, then
>>> 11..15.
>>>   
>>>       
>> Does this help? 
>>
>> Python 2.5.4 (r254:67916, Dec 23 2008, 15:10:54) [MSC v.1310 32 bit 
>> (Intel)] on win32
>> Type "help", "copyright", "credits" or "license" for more information.
>>  >>> a = [4, 0, 11]
>>  >>> b = [11, 4, 15]
>>  >>> zip(a,b)
>> [(4, 11), (0, 4), (11, 15)]
>>  >>>
>>     
>
> Mhm, I got this far. But how do I get from here to a single index array
>
> [ 4, 5, 6, ... 10, 0, 1, 2, 3, 11, 12, 13, 14 ] ?
>
>   
not sure I understand your goal ... is this what you want:
 >>> [range(i,j) for i,j in zip(a,b)]
[[4, 5, 6, 7, 8, 9, 10], [0, 1, 2, 3], [11, 12, 13, 14]]
 >>>
> Greetings
> Raik
>
>   
>
>
>
>   
>> Apologies if I'm stating the obvious.
>>
>> -- jv
>>     
>>> In reality, a and b have 10000+ elements and the arrays to be "sliced" are very
>>> large so I want to avoid any for loops etc. Any idea how this could be done? I
>>> thought some combination of *repeat* and adding of *arange* should do the trick
>>> but just cannot nail it down.
>>>
>>> Thanks in advance for any hints!
>>>
>>> Greetings,
>>> Raik
>>>
>>>
>>> _______________________________________________
>>> Numpy-discussion mailing list
>>> Numpy-discussion@scipy.org
>>> http://projects.scipy.org/mailman/listinfo/numpy-discussion
>>>   
>>>       
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>>
>>     
>
>   

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