If I have a view into part of numpy array:
import numpy as np
array = np.arange(10)
view = array[4:8]
Can I access element to the left (in memory) of first view element, using only view identifier?
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If your array is referencing the indices of [4:8] you should be able to access it with view[0] index over the array.Harsha TJ– Harsha TJ2021-08-18 14:18:42 +00:00Commented Aug 18, 2021 at 14:18
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1 Answer
view keeps a reference to array in the base attribute. view.base is array.
Thus, you could access this identifier by calling left_element = view.base[3].
If you don't know the offset of 4 that generated the view in this case, you may be able to reconstruct it by looking at raw pointers in the array interface, or simply the byte_bounds. This is easily done in this tiny example, but might be harder to get right when non-contiguous multidimensional arrays are in play, or in a different orders.
For your 1D example you could use:
offset_bytes = np.byte_bounds(view)[0] - np.byte_bounds(view.base)[0]
offset = offset_bytes // view.strides[0]
left_element = view.base[offset - 1]
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