The track-best Reference Manual

Table of Contents

The track-best Reference Manual

This is the track-best Reference Manual, version 0.1.20130509, generated automatically by Declt version 2.4 "Will Decker" on Wed Jun 20 12:40:37 2018 GMT+0.

1 Introduction

Track-Best Library

Track-Best is a Common Lisp library used to track the N best of some series of items. One creates a tracker and then adds scored items to it. The tracker keeps the N best items and returns them at the end.

The main entry point is the function WITH-TRACK-BEST macro.

(with-track-best (keyword-args)
   ...body...)

The body can call (track item score &optional tracker) as often as desired. In the end, the with-track-best will return two values: the list of best items and the list of their scores.

The keyword-args can be any of the following:

• :NAME variable-name --- A symbol used as the variable name for the tracker. This is only needed if you will explicitly refer to the tracker in the body statements.
• :KEEP number-to-keep --- The number of items to track. This defaults to 1 item.
• :ORDER-BY-FN function-to-compare-scores --- The function used to determine if one score is larger or smaller than another score. The default for this argument is #'>
• :SINGLE t-or-nil --- If single is true and keep is 1, then only return the best item rather than a list containing the best item. The default for this argument is T.
• :RETURN-BEST t-or-nil --- if return-best is NIL, then the form returns the value(s) from the last expression in the body rather than the best items. This argument defaults to T. Note: This argument is evaluated at macroexpansion time, not at runtime.

Example: Finding the longest matching substring in two strings

Given two strings S1 and S2, find the longest substring they have in common.

(let ((s1 "Keep playing cards on Friday.  Get smart.")
      (s2 "Thank G-d it's Friday!"))
  (with-track-best ()
    (dotimes (len (length s1))
      (dotimes (offset (- (length s1) len -1))
        (let ((needle (subseq s1 offset (+ offset len))))
          (when (search needle s2 :test #'string=)
            (track needle len)))))))

The outer DOTIMES loop determines the length substring of S1 to look for in S2. The inner DOTIMES loop picks the offset to start the substring of S1. Then, if the substring is found in S2, it is tracked with its score being its length.

Example: Finding the farthest vertex from a point

Given a list of vertexes VERTEX-LIST, find the vertex farthest from a TARGET vertex based on a given DISTANCE function.

(defun find-farthest (target vertex-list distance-fn)
  (with-track-best ()
    (dolist (v vertex-list)
      (track v (funcall distance-fn v target))))))

Example: Finding the three closest vertexes to a point

Given a list of vertexes VERTEX-LIST, find the three that are closest to a TARGET vertex based on a given DISTANCE function.

(defun find-three-closest (target vertex-list distance-fn)
  (with-track-best (:keep 3 :order-by-fn #'<)
    (dolist (v vertex-list)
      (track v (funcall distance-fn v target))))))

The :ORDER-BY-FN function here specifies that the best vectors are the ones with the smallest score. The scores used here are the distance from the TARGET as given by the DISTANCE-FN.

Example: The lowest highest point

Suppose you had a list of various states. For each state you had a list of different cities and their altitude. Find the highest altitude in each state and find the state with the lowest high.

(let ((data '(("Alabama"  ("Birmingham" 664)
                          ("Mobile" 218)
                          ("Montegomery" 221))
              ("Alaska"   ("Anchorage" 144)
                          ("Fairbanks" 531))
              ("Arizona"  ("Grand Canyon" 6606)
                          ("Phoenix" 1132)
                          ("Tuscon"  2641)))))
  (with-track-best (:order-by-fn #'<)
    (dolist (state-info data)
      (multiple-value-bind (city altitude)
          (with-track-best ()
            (dolist (city-info (rest state-info))
              (track (first city-info) (second city-info))))
        (track (list (first state-info) city) altitude)))))

 => (values '("Alaska" "Fairbanks") 531)

The inner DOLIST here tracks the highest city in a given state. The outer DOLIST trackes the lowest of the highest cities.

Example: Finding the lowest and highest numbers in a list

Given a list of numbers, return a list containing the lowest number and highest number from the list.

(with-track-best (:name lowest
                  :order-by-fn #'<
                  :return-best nil)
  (with-track-best (:name highest
                    :return-best nil)
    (dolist (v '(2 4 6 8 10 1 3 5 7 9))
      (track v v lowest)
      (track v v highest))

    (list (first (map-best #'cons lowest))
          (first (map-best #'cons highest)))))

In this example, we used the :NAME to specify two different trackers. In our loop, we tracked each value with both trackers. In the end, we also used the :RETURN-RESULTS NIL directive so that the returned value would be our LIST expression rather than the best result from the LOWEST tracker.

Warning about how ties are handled

If the :KEEP parameter is 1, the first item tracked with the best score will be returned. If the :KEEP parameter is greater than one, there is no guarantee about which items are kept when multiple items of the same score are found. For example, the following form will definitely return (VALUES :EIGHT 8).

(with-track-best ()
  (dolist (c '((:FIVE 5)  (:EIGHT 8)
               (:CINQO 5) (:OCHO 8)
               (:CINQ 5)  (:HUIT 8)))
    (track (first c) (second c))))

=> (values :EIGHT 8)

On the other hand, this snippet will not guarantee the order in which :EIGHT, :OCHO, and :HUIT appear nor which of :FIVE, :CINQO, or :CINQ will be included.

(with-track-best (:keep 4)
  (dolist (c '((:FIVE 5)  (:EIGHT 8)
               (:CINQO 5) (:OCHO 8)
               (:CINQ 5)  (:HUIT 8)))
    (track (first c) (second c))))

=> (values ??? '(8 8 8 5))

To be sure, the answer is deterministic. Given the same inputs in the same order, the same output will be generated. There are two caveats to this:

• Where a tie gets inserted amongst its peers is highly sensitive to the number of items being kept and where its peers are in the list at the time of insertion.
• More importantly, I make no guarantee that this order will be preserved across releases. You should not depend on particular behavior when :KEEP is greater than one.

2 Systems

The main system appears first, followed by any subsystem dependency.

2.1 track-best

Author

Patrick Stein <pat@nklein.com>

License

Free

Description

Macros/functions for tracking the best items. See the README.md for more details.

Version

0.1.20130509

Source

track-best.asd (file)

Components

• readme.md (file)
• src (module)

3 Modules

Modules are listed depth-first from the system components tree.

3.1 track-best/src

Parent

track-best (system)

Location

src/

Components

• package.lisp (file)
• types.lisp (file)
• globals.lisp (file)
• insert.lisp (file)
• methods.lisp (file)
• track-best.lisp (file)

4 Files

Files are sorted by type and then listed depth-first from the systems components trees.

4.1 Lisp

4.1.1 track-best.asd

Location

track-best.asd

Systems

track-best (system)

4.1.2 track-best/src/package.lisp

Parent

src (module)

Location

src/package.lisp

Packages

track-best

4.1.3 track-best/src/types.lisp

Dependency

package.lisp (file)

Parent

src (module)

Location

src/types.lisp

Internal Definitions

• best-item (structure)
• best-item-array (type)
• best-item-item (function)
• best-item-p (function)
• best-item-score (function)
• best-tracker (structure)
• best-tracker-best (function)
• (setf best-tracker-best) (function)
• best-tracker-keep (function)
• best-tracker-order-by-fn (function)
• best-tracker-p (function)
• copy-best-item (function)
• copy-best-tracker (function)
• make-best-item (function)
• make-best-tracker (function)
• order-by-fn (type)

4.1.4 track-best/src/globals.lisp

Dependency

types.lisp (file)

Parent

src (module)

Location

src/globals.lisp

Internal Definitions

*current-best-tracker* (special variable)

4.1.5 track-best/src/insert.lisp

Dependency

globals.lisp (file)

Parent

src (module)

Location

src/insert.lisp

Internal Definitions

insert-tracked-item (function)

4.1.6 track-best/src/methods.lisp

Dependency

insert.lisp (file)

Parent

src (module)

Location

src/methods.lisp

Exported Definitions

• map-best (function)
• track (function)

4.1.7 track-best/src/track-best.lisp

Dependency

methods.lisp (file)

Parent

src (module)

Location

src/track-best.lisp

Exported Definitions

with-track-best (macro)

4.2 Other

4.2.1 track-best/README.md

Parent

track-best (system)

Location

README.md

5 Packages

Packages are listed by definition order.

5.1 track-best

Source

package.lisp (file)

Use List

common-lisp

Exported Definitions

• map-best (function)
• track (function)
• with-track-best (macro)

Internal Definitions

• *current-best-tracker* (special variable)
• best-item (structure)
• best-item-array (type)
• best-item-item (function)
• best-item-p (function)
• best-item-score (function)
• best-tracker (structure)
• best-tracker-best (function)
• (setf best-tracker-best) (function)
• best-tracker-keep (function)
• best-tracker-order-by-fn (function)
• best-tracker-p (function)
• copy-best-item (function)
• copy-best-tracker (function)
• insert-tracked-item (function)
• make-best-item (function)
• make-best-tracker (function)
• order-by-fn (type)

6 Definitions

Definitions are sorted by export status, category, package, and then by lexicographic order.

6.1 Exported definitions

6.1.1 Macros

Macro: with-track-best (&key NAME KEEP ORDER-BY-FN ALWAYS-RETURN-LIST RETURN-BEST) &body BODY

Package

track-best

Source

track-best.lisp (file)

6.1.2 Functions

Function: map-best FN &optional TRACKER

Package

track-best

Source

methods.lisp (file)

Function: track ITEM SCORE &optional TRACKER

Add the ITEM with SCORE to the TRACKER.

Package

track-best

Source

methods.lisp (file)

6.2 Internal definitions

6.2.1 Special variables

Special Variable: *current-best-tracker*

The current best-tracker instance.

Package

track-best

Source

globals.lisp (file)

6.2.2 Functions

Function: best-item-item INSTANCE

Package

track-best

Source

types.lisp (file)

Function: best-item-p OBJECT

Package

track-best

Source

types.lisp (file)

Function: best-item-score INSTANCE

Package

track-best

Source

types.lisp (file)

Function: best-tracker-best INSTANCE

Function: (setf best-tracker-best) VALUE INSTANCE

Package

track-best

Source

types.lisp (file)

Function: best-tracker-keep INSTANCE

Package

track-best

Source

types.lisp (file)

Function: best-tracker-order-by-fn INSTANCE

Package

track-best

Source

types.lisp (file)

Function: best-tracker-p OBJECT

Package

track-best

Source

types.lisp (file)

Function: copy-best-item INSTANCE

Package

track-best

Source

types.lisp (file)

Function: copy-best-tracker INSTANCE

Package

track-best

Source

types.lisp (file)

Function: insert-tracked-item TRACKER ITEM &optional ALWAYS

Insert the ITEM into the TRACKER. If ALWAYS is true, then do it even though it is not bigger than the last thing in the array.

Package

track-best

Source

insert.lisp (file)

Function: make-best-item &key (SCORE SCORE) (ITEM ITEM)

Package

track-best

Source

types.lisp (file)

Function: make-best-tracker &key (BEST BEST) (KEEP KEEP) (ORDER-BY-FN ORDER-BY-FN)

Package

track-best

Source

types.lisp (file)

6.2.3 Structures

Structure: best-item ()

Package

track-best

Source

types.lisp (file)

Direct superclasses

structure-object (structure)

Direct slots

Slot: score

Initform

0.0

Readers

best-item-score (function)

Writers

(setf best-item-score) (function)

Slot: item

Readers

best-item-item (function)

Writers

(setf best-item-item) (function)

Structure: best-tracker ()

Package

track-best

Source

types.lisp (file)

Direct superclasses

structure-object (structure)

Direct slots

Slot: best

Type

track-best::best-item-array

Initform

(make-array 0 :element-type (quote track-best::best-item) :adjustable t)

Readers

best-tracker-best (function)

Writers

(setf best-tracker-best) (function)

Slot: keep

Initform

1

Readers

best-tracker-keep (function)

Writers

(setf best-tracker-keep) (function)

Slot: order-by-fn

Type

track-best::order-by-fn

Initform

(function >)

Readers

best-tracker-order-by-fn (function)

Writers

(setf best-tracker-order-by-fn) (function)

6.2.4 Types

Type: best-item-array &optional LENGTH

Type for an array of BEST-ITEM instances.

Package

track-best

Source

types.lisp (file)

Type: order-by-fn ()

Package

track-best

Source

types.lisp (file)

Appendix A Indexes

A.1 Concepts

A.2 Functions

A.3 Variables

A.4 Data types