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Name

THIS IS NOT YET AN OFFICIAL MOCHIKIT COMPONENT

MochiKit.Bisect - Array bisection algorithm

Availability:
Available in MochiKit 1.5+

Synopsis

// Locate the leftmost value exactly equal to x
function index(a, x) {
    var i = bisectLeft(a, x);
    if (i != a.length && a[i] == x)
        return i;
    return NotFound;
}

// Find rightmost value less than x
function find_lt(a, x) {
    var i = bisectLeft(a, x);
    if (i != 0)
        return a[i-1];
    return NotFound;
}

// Find rightmost value less than or equal to x
function find_le(a, x) {
    var i = bisectRight(a, x);
    if (i != 0)
        return a[i-1];
    return NotFound;
}

// Find leftmost value greater than x
function find_gt(a, x) {
    var i = bisectRight(a, x);
    if (i != a.length)
        return a[i];
    return NotFound;
}

// Find leftmost item greater than or equal to x
function find_ge(a, x) {
    var i = bisectLeft(a, x);
    if (i != a.length)
        return a[i];
    return NotFound;
}

function grade(score, breakpoints, grades) {
    breakpoints = breakpoints || [60, 70, 80, 90];
    grades = grades || ['F','D','C','B','A'];

    var i = bisect(breakpoints, score);
    return grades[i];
}

>> map(grade, [33, 99, 77, 70, 89, 90, 100]);
    --> ['F', 'A', 'C', 'C', 'B', 'A', 'A']

Description

This module provides support for maintaining a list in sorted order without having to sort the list after each insertion. For long lists of items with expensive comparison operations, this can be an improvement over the more common approach. The module is called bisect because it uses a basic bisection algorithm [1] to do its work. The source code may be most useful as a working example of the algorithm (the boundary conditions are already right!).

Currently this is basically a clone/port of the Python bisect [3] module, http://docs.python.org/library/bisect.html

Dependencies

Overview

TODO: ...

API Reference

Functions

bisectLeft(a, x[, lo=0, hi=a.length]):

Locate the insertion point for x in a 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 x is already present in a, 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.splice() assuming that a is already sorted.

The returned insertion point i partitions the array a into two halves so that all(val < x for val in a[lo:i]) for the left side and all(val >= x for val in a[i:hi]) for the right side.

insortLeft(a, x[, lo=0, hi=a.length]):

Insert x in a in sorted order. This is equivalent to a.splice(bisectLeft(a, x, lo, hi), 0, x) assuming that a is already sorted. Keep in mind that the O(log n) search is dominated by the slow O(n) insertion step.

bisectRight(a, x[, lo=0, hi=a.length]):

Similar to bisectLeft(), but returns an insertion point which comes after (to the right of) any existing entries of x in a.

The returned insertion point i partitions the array a into two halves so that all(val <= x for val in a[lo:i]) for the left side and all(val > x for val in a[i:hi]) for the right side.

Also available via the bisect alias.

bisect(a, x[, lo=0, hi=a.length]):

Alias for bisectRight()

insortRight(a, x[, lo=0, hi=a.length]):

Similar to insortLeft(), but inserting x in a after any existing entries of x.

Also available via the insort alias.

insort(a, x[, lo=0, hi=a.length]):

Alias for insortRight()

See Also

[1]Bisection method: http://en.wikipedia.org/wiki/Bisection_method
[2]Binary search: http://en.wikipedia.org/wiki/Binary_search
[3]Python bisect module: http://docs.python.org/library/bisect.html

Authors