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up vote 2 down vote favorite

I want the last 4 values of this equation.

Is there a better way to this in one step, like modifying the equation or another extraction technique other than using delete

a=5
d=2

n = np.cumsum(d ** np.arange(1, a+1))
print 'n=', n
n = np.delete(n,0)
print 'n extracted=', n

n= [ 2  6 14 30 62]
n extracted= [ 6 14 30 62]
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1 Answer

up vote 7 down vote accepted 
print n[-4::]

will print the last 4 elements. You can do all kinds of array slicing like this, the above was just an example. You can index the array from the front or the back.

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you should note that in this case the second : is optional –  MattDMo 16 hours ago
 
Then that would mean I can also do this n = n[1:] Which way is more efficient in terms of performance slicing or deleting. –  user3084006 16 hours ago
 
@user3084006 Is this the actual use case or is this a simplified example? I mean, do you always just have to remove the first element out of a 5 element list? Or will you have to remove 50 elements from a 20000 element list (for example)? –  Cyber 16 hours ago
 
@Cyber it is a simplified case. I am just trying to remove x elements out something like n=n[len(n)-x,:], n = np.delete(n,index), index=[x] –  user3084006 16 hours ago
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