Extracting indices from numpy array python

Question

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]

Cory Kramer · Accepted Answer · 2013-12-31 20:09:52Z

7

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.

answered Dec 31, 2013 at 20:09

Cory Kramer

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4 Comments

MattDMo Over a year ago

you should note that in this case the second : is optional

user3084006 Over a year 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.

Cory Kramer Over a year 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)?

user3084006 Over a year 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]

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