How to find the index of n largest elements in a list or np.array, Python
Maybe something like:
>>> K
[4, 5, 1, 6, 2, 5, 2, 10]
>>> sorted(range(len(K)), key=lambda x: K[x])
[2, 4, 6, 0, 1, 5, 3, 7]
>>> sorted(range(len(K)), key=lambda x: K[x])[-5:]
[0, 1, 5, 3, 7]
or using numpy
, you can use argsort
:
>>> np.argsort(K)[-5:]
array([0, 1, 5, 3, 7])
argsort
is also a method:
>>> K = np.array(K)
>>> K.argsort()[-5:]
array([0, 1, 5, 3, 7])
>>> K[K.argsort()[-5:]]
array([ 4, 5, 5, 6, 10])
Consider the following code,
N=5
K = [1,10,2,4,5,5,6,2]
#store list in tmp to retrieve index
tmp=list(K)
#sort list so that largest elements are on the far right
K.sort()
#To get the 5 largest elements
print K[-N:]
#To get the 5th largest element
print K[-N]
#get index of the 5th largest element
print tmp.index(K[-N])
If you wish to ignore duplicates, then use set() as follows,
N=5
K = [1,10,2,4,5,5,6,2]
#store list in tmp to retrieve index
tmp=list(K)
#sort list so that largest elements are on the far right
K.sort()
#Putting the list to a set removes duplicates
K=set(K)
#change K back to list since set does not support indexing
K=list(K)
#To get the 5 largest elements
print K[-N:]
#To get the 5th largest element
print K[-N]
#get index of the 5th largest element
print tmp.index(K[-N])
Hopefully one of them covers your question :)
This should work:
K = [1,2,2,4,5,5,6,10]
num = 5
print 'K %s.' % (sorted(K, reverse=True)[:num])