[Numpy-discussion] Find the N maximum values and corresponding indexes in an array
Howard Chong
hgchong@berkeley....
Wed Dec 2 17:55:00 CST 2009
I will need to find the N largest numbers and corresponding indexes in an
1-D array.
If N==1, I can easily do:
def myFindMaxC(myList):
"""implement finding maximum value with using numpy.array()"""
myA=np.array(myList)
maxIndex=myA.argmax()
maxVal=myA[maxIndex]
return [maxIndex, maxVal]
For me, I'm likely going to be running this with N==7.
So, I think I have to iterate over the array. Doing it with non-numpy
procedures is **quite slow**. Here, I run it with N==1 without using any
numpy procedures.
def myFindMaxA(myList):
"""implement finding maximum value with for loop iteration"""
maxIndex=0
maxVal=myList[0]
for index, item in enumerate(myList):
if item[0]>maxVal:
maxVal=item[0]
maxIndex=index
return [maxIndex, maxVal]
My question is: how can I make the latter version run faster? I think the
answer is that I have to do the iteration in C.
If that's the case, can anyone point me to where np.array.argmax() is
implemented so I can write np.array.argmaxN() extend it to the N largest
values?
Thanks!
--
Howard Chong
Dept. of Agricultural and Resource Economics and Energy Institute @ Haas
Business School
UC Berkeley
hgchong@berkeley.edu
Cell: 510-333-0539
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.scipy.org/pipermail/numpy-discussion/attachments/20091202/1d121a34/attachment-0001.html
More information about the NumPy-Discussion
mailing list