Summing array values over a specific range with numpy

Question

So I am trying to get the sum over a specific range of values in a text file using:

np.sum(d[a:b])

I am using a text file with 10000 entries. I know that we always start at zero. So my range is quite large i.e; index 200-555 (including 200 and 555). I tried just for testing summing over a small range:

In [17]: np.sum(d[1:4])
Out[17]: 50.164228

But the above code summed from the 2nd block (labeled number 1 by python) until the third. The numbers are; (0-> 13.024) , 1-> 17.4529, 2-> 16.9382, 3-> 15.7731,( 4-> 11.7589), 5-> 14.5178.

zero is just for reference and it ignored the 4th-> 11.7589. Why?

Answer 1

When using range indexing in Python, the second index (the 4 in your case) is not an inclusive index. By specifying [1:4], you're summing the elements from index 1 up to but not including index 4. Specify 5 as the second index if you want to include the element at index 4.