bisect.md

bisect

Array bisection algorithm

import bisect

Method	Description
bisect.bisect_left(list, item[, lo[, hi]])	Locate the proper insertion point for item in list to maintain sorted order. The parameters lo and hi may be used to specify a subset of the list which should be considered; by default the entire list is used. If item is already present in list, the insertion point will be before (to the left of) any existing entries. The return value is suitable for use as the first parameter to list.insert(). This assumes that list is already sorted.
bisect.bisect_right(list, item[, lo[, hi]])	Similar to bisect_left(), but returns an insertion point which comes after (to the right of) any existing entries of item in list.

     |

| bisect.bisect(...) | Alias for bisect.bisect_right(...) | | bisect.insort_left(list, item[, lo[, hi]]) | Insert item in list in sorted order. This is equivalent to list.insert(bisect.bisect_left(list, item, lo, hi), item). This assumes that list is already sorted. | | bisect.insort_right(list, item[, lo[, hi]]) | Similar to insort_left(), but inserting item in list after any existing entries of item. | | bisect.insort(...) | Alias for bisect.insort_right(...) |

Bisection Algorithm Example

grades = "FEDCBA"
breakpoints = [30, 44, 66, 75, 85]
from bisect import bisect
def grade(total):
    return grades[bisect(breakpoints, total)]

grade(66)
Out[]:
'C'

map(grade, [33, 99, 77, 44, 12, 88])

Out[]:
['E', 'A', 'B', 'D', 'F', 'A']

import bisect
def binary_search(A, B):
    clip = lambda idx: max(min(len(A) - 1, idx), 0)
    C = []
    for b in B:
        idx = bisect.bisect(A, b)
        # A[idx-1] < b <= A[idx]
        C.append(closer(A[clip(idx - 1)], A[clip(idx)], b))
    return C