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])
>
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>
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