How to extract an n size window substring from any string?-CodePudding

Given a list of elements, how to create a window of an arbitrary size, and extract n elements to the left and right from the center? For example, given:

l = ['This', 'document', 'is', 'the', 'second', 'document']

and a window = 2

How to extract the following sublist:

['document', 'is', 'the', 'second', 'document']

So far I tried to:

middle = int((len(l)/2))

middle_element = l[middle]
middle_index = l.index(l[middle])

left_side = l[:middle_index]
right_side = l[middle_index:]
sublist = left_side right_side

The problem with my approach is that it doesnt work for any list of any size. How should I control sliding from the left and right once I find the center of the list?

CodePudding user response：

Here is a way to do what your question asks:

l = ['This', 'document', 'is', 'the', 'second', 'document']
window = 2
middle = int((len(l)/2))
sublist = l[max(0, middle - window):min(len(l), middle   window   1)]

Output:

['document', 'is', 'the', 'second', 'document']

Explanation:

We take a slice of l starting at middle - window (but no less than 0 as enforced using max()). Ignoring edge cases, this ensures we get middle - window, middle - window 1, ..., middle - window window which are a total of window 1 list items (numbering window items to the left of middle in addition to the item at index middle). Our slice ends at middle window 1 (guarded against going out of range by min(), though technically this is not required as slices are forgiving of end-of-range values greater than the sequence length) which, in addition to the items already accounted for above, adds the items middle 1, ..., middle window (but not the item middle window 1 as slice notation does not include the end of the slice range) which count for an additional window items to the right of the the middle index.