Editing Lookup table (section)

== History ==
[[File:Abramowitz&Stegun.page97.agr.jpg|thumb|Part of a 20th-century table of [[common logarithm]]s in the reference book [[Abramowitz and Stegun]].]]
Before the advent of computers, lookup tables of values were used to speed up hand calculations of complex functions, such as in [[trigonometry]], [[common logarithm|logarithms]], and statistical density functions.<ref>{{cite book
|editor1-last= Campbell-Kelly
|editor1-first= Martin|editor1-link=Martin Campbell-Kelly
|editor2-last= Croarken
|editor2-first= Mary|editor2-link=Mary Croarken
|editor3-last= Robson
|editor3-first= Eleanor|editor3-link=Eleanor Robson
|title=  The History of Mathematical Tables: From Sumer to Spreadsheets
|title-link= The History of Mathematical Tables
|year=  2003
|publisher=Oxford University Press
}}
</ref>

In ancient (499 AD) India, [[Aryabhata]] created one of the first [[Āryabhaṭa's sine table|sine tables]], which he encoded in a Sanskrit-letter-based number system. In 493 AD, [[Victorius of Aquitaine]] wrote a 98-column multiplication table which gave (in [[Roman numerals]]) the product of every number from 2 to 50 times and the rows were "a list of numbers starting with one thousand, descending by hundreds to one hundred, then descending by tens to ten, then by ones to one, and then the fractions down to 1/144"<ref>Maher, David. W. J. and John F. Makowski. "[https://ecommons.luc.edu/cgi/viewcontent.cgi?article=1024&context=classicalstudies_facpubs Literary Evidence for Roman Arithmetic With Fractions]", 'Classical Philology' (2001) Vol. 96 No. 4 (2001) pp. 376–399. (See page p.383.)</ref> Modern school children are often taught to memorize "[[multiplication table|times tables]]" to avoid calculations of the most commonly used numbers (up to 9 x 9 or 12 x 12).

Early in the history of computers, [[input/output]] operations were particularly slow – even in comparison to processor speeds of the time. It made sense to reduce expensive read operations by a form of manual [[cache (computing)|caching]] by creating either static lookup tables (embedded in the program) or dynamic prefetched arrays to contain only the most commonly occurring data items. Despite the introduction of systemwide caching that now automates this process, application level lookup tables can still improve performance for data items that rarely, if ever, change.

Lookup tables were one of the earliest functionalities implemented in computer [[spreadsheet]]s, with the initial version of [[VisiCalc]] (1979) including a <code>LOOKUP</code> function among its original 20 functions.<ref>[https://vlookupweek.wordpress.com/2012/03/31/bill-jelen-from-1979-visicalc-and-lookup/ Bill Jelen: "From 1979 – VisiCalc and LOOKUP"!], by MrExcel East, 31 March 2012</ref> This has been followed by subsequent spreadsheets, such as [[Microsoft Excel]], and complemented by specialized <code>VLOOKUP</code> and <code>HLOOKUP</code> functions to simplify lookup in a vertical or horizontal table. In Microsoft Excel the <code>XLOOKUP</code> function has been rolled out starting 28 August 2019.