84 lines
3.0 KiB
TeX
84 lines
3.0 KiB
TeX
\section{\module{bisect} ---
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Array bisection algorithm}
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\declaremodule{standard}{bisect}
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\modulesynopsis{Array bisection algorithms for binary searching.}
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\sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}
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% LaTeX produced by Fred L. Drake, Jr. <fdrake@acm.org>, with an
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% example based on the PyModules FAQ entry by Aaron Watters
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% <arw@pythonpros.com>.
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This module provides support for maintaining a list in sorted order
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without having to sort the list after each insertion. For long lists
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of items with expensive comparison operations, this can be an
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improvement over the more common approach. The module is called
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\module{bisect} because it uses a basic bisection algorithm to do its
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work. The source code may be most useful as a working example of the
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algorithm (the boundary conditions are already right!).
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The following functions are provided:
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\begin{funcdesc}{bisect_left}{list, item\optional{, lo\optional{, hi}}}
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Locate the proper insertion point for \var{item} in \var{list} to
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maintain sorted order. The parameters \var{lo} and \var{hi} may be
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used to specify a subset of the list which should be considered; by
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default the entire list is used. If \var{item} is already present
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in \var{list}, the insertion point will be before (to the left of)
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any existing entries. The return value is suitable for use as the
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first parameter to \code{\var{list}.insert()}. This assumes that
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\var{list} is already sorted.
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\versionadded{2.1}
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\end{funcdesc}
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\begin{funcdesc}{bisect_right}{list, item\optional{, lo\optional{, hi}}}
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Similar to \function{bisect_left()}, but returns an insertion point
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which comes after (to the right of) any existing entries of
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\var{item} in \var{list}.
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\versionadded{2.1}
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\end{funcdesc}
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\begin{funcdesc}{bisect}{\unspecified}
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Alias for \function{bisect_right()}.
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\end{funcdesc}
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\begin{funcdesc}{insort_left}{list, item\optional{, lo\optional{, hi}}}
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Insert \var{item} in \var{list} in sorted order. This is equivalent
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to \code{\var{list}.insert(bisect.bisect_left(\var{list}, \var{item},
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\var{lo}, \var{hi}), \var{item})}. This assumes that \var{list} is
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already sorted.
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\versionadded{2.1}
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\end{funcdesc}
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\begin{funcdesc}{insort_right}{list, item\optional{, lo\optional{, hi}}}
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Similar to \function{insort_left()}, but inserting \var{item} in
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\var{list} after any existing entries of \var{item}.
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\versionadded{2.1}
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\end{funcdesc}
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\begin{funcdesc}{insort}{\unspecified}
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Alias for \function{insort_right()}.
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\end{funcdesc}
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\subsection{Example}
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\nodename{bisect-example}
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The \function{bisect()} function is generally useful for categorizing
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numeric data. This example uses \function{bisect()} to look up a
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letter grade for an exam total (say) based on a set of ordered numeric
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breakpoints: 85 and up is an `A', 75..84 is a `B', etc.
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\begin{verbatim}
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>>> grades = "FEDCBA"
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>>> breakpoints = [30, 44, 66, 75, 85]
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>>> from bisect import bisect
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>>> def grade(total):
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... return grades[bisect(breakpoints, total)]
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...
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>>> grade(66)
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'C'
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>>> map(grade, [33, 99, 77, 44, 12, 88])
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['E', 'A', 'B', 'D', 'F', 'A']
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\end{verbatim}
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