[Numpy-discussion] strange behavior of variable

Sudheer Joseph sudheer.joseph@yahoo....
Sun Aug 18 04:06:19 CDT 2013



 
However, I was looking for the indices of the biggest 3 numbers which can be used to find corresponding values in another vector, which made me to write the function. Is there a smarter way for getting indices?
with best regards,
Sudheer
Thanks a lot Eric,

                    Here comes the smartness of python!!, I am just climbing the bottom steps...
>with best regards,
>Sudheer
>
>
>
> 
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>Sudheer Joseph 
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>>________________________________
>> From: Eric Firing <efiring@hawaii.edu>
>>To: numpy-discussion@scipy.org 
>>Sent: Sunday, 18 August 2013 1:57 PM
>>Subject: Re: [Numpy-discussion] strange behavior of variable
>> 
>>
>>On 2013/08/17 9:49 PM, Sudheer Joseph wrote:
>>>
 Hi,
>>>           I have defined a small function to find the n maximum values
>>> of an array as below. With in it I assign the input array to a second
>>> array and temporarily make the array location after first iteration as
>>> nan. I expected this temporary change to be limited to the second
>>> variable. However my initial variable gets modified. Can any one through
>>> some light to what is happening here?. In case of matlab this logic works.
>>>
>>> ######
>>> #FUNCTION maxn
>>> ######
>>> import numpy as np
>>> def max_n(a,n):
>>>       b=a
>>
>>This is not making "b" a copy of "a", it is simply making it an alias 
>>for it.  To make it a copy you could use "b = a[:]", or "b = a.copy()"
>>
>>It sounds like you don't really need a function, however.  Try this:
>>
>># test data:
>>a = np.random.randn(10)
>>n = 2
>>
>># One-line
 solution:
>>biggest_n = np.sort(a)[-n:]
>>
>>print a
>>print biggest_n
>>
>>If you want them ordered from largest to smallest, just reverse the list:
>>
>>biggest_n = biggest_n[::-1]
>>
>>Eric
>>
>>
>>>       result=[]
>>>       for i in np.arange(1,n+1):
>>>           mxidx=np.where(b==max(b))
>>>           result.append(mxidx)
>>>           b[mxidx]=np.nan
>>>       result=np.ravel(result)
>>>       return(result)
>>>
>>> ### TEST
>>> In [8]: x=np.arange(float(0),10)
>>>
>>> In [9]: max
>>> max    max_n
>>>
>>> In [9]: max_n(x,2)
>>> Out[9]: array([9, 8])
>>>
>>> In [10]: x
>>> Out[10]: array([  0.,   1.,   2.,   3.,   4.,   5.,   6.,   7.,  nan,  nan])
>>>
 ***************************************************************
>>> Sudheer Joseph
>>> Indian National Centre for Ocean Information Services
>>> Ministry of Earth Sciences, Govt. of India
>>> POST BOX NO: 21, IDA Jeedeemetla P.O.
>>> Via Pragathi Nagar,Kukatpally, Hyderabad; Pin:5000 55
>>> Tel:+91-40-23886047(O),Fax:+91-40-23895011(O),
>>> Tel:+91-40-23044600(R),Tel:+91-40-9440832534(Mobile)
>>> E-mail:sjo.India@gmail.com;sudheer.joseph@yahoo.com
>>> Web- http://oppamthadathil.tripod.com
>>> ***************************************************************
>>>
>>>
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>>
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