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External sort: Difference between revisions
→{{header|REXX}}: added the REXX computer programming language for this task.
(→{{header|REXX}}: added the REXX computer programming language for this task.) |
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example()
</lang>
=={{header|REXX}}==
Programming note: the method used to generate the input file is to generate '''N''' records,
<br>breaking up the records into sort work files of no more than '''10''' records (limit).
<br>The sort work files are then sorted with an external sort, and then merged into one big file.
<lang rexx>/*REXX pgm reads a file, splits into smaller files, sorts 'em, combines into sorted file*/
parse arg FID n lim seed . /*obtain optional arguments from the CL*/
if FID=='' | FID=="," then FID= 'SORT_EXT.OUT' /*name of the output (sorted) file. */
if n=='' | n=="," then n= 500 /*number of records (rand #s) to gen. */
if lim=='' | lim=="," then lim= 10 /*number of records per SORTWORK file. */
if datatype(seed, 'W') then call random ,,seed /*Numeric? Then use it as a rand seed.*/
sWork = 'SORTWORK.' /*the filename of the SORTWORK files.*/
call gen n,lim /*generate SORTWORK.nnn files. */
call srt # /*sort records in all SORTWORK files.*/
call mrg /*merge records in the SORTWORK files.*/
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
mrg: procedure expose FID sWork; parse arg # /*#: the number of SORTWORK files. */
@.= copies('ff'x, 1e5) /*no value should be larger than this. */
call lineout FID, , 1 /*position the output file at rec # 1. */
do j=1 until @.j==@.; call rdr j /*read any number of SORTWORK files, */
end /*j*/ /*but initially just 1 record per file.*/
j=j-1 /*adj. J; read from a non─existent file*/
do forever; y=@.; z=0 /*find the lowest value for N values.*/
do k=1 for j /*traipse through the stemmed @ array.*/
if @.k==@. then call rdr k /*Not defined? Then read a file record*/
if @.k<<y then do; y=@.k; z=k; end /*Lowest so far? Then mark this as min.*/
end /*k*/ /* [↑] note use of << exact comparison*/
if z==0 then leave /*Any more records? No, close file. */
call lineout FID, @.z /*write the value to the output file. */
call rdr z /*re-populate a value from the # file. */
end /*forever*/ /*keep reading/merging until exhausted.*/
call lineout FID /*close the output file (just in case).*/
'DEL' sWORK"*" /*delete all the SORTWORK files. */
return
/*──────────────────────────────────────────────────────────────────────────────────────*/
gen: procedure expose #; parse arg m,siz; d= digits() /*for justify. */
# = 0 /*number of SORTWORK.nnn files so far*/
do j=1 for m; #= 1 + j % siz /*create workfile#*/
call lineout 'SORTWORK.'#, right(random(, 1e5), d) /*write rand #. */
end /*j*/
do k=1 for #; call lineout 'SORTWORK.'#; end /*close a workfile*/
return
/*──────────────────────────────────────────────────────────────────────────────────────*/
rdr: parse arg a; @.a=@.; f=sWork||a; if lines(f)\==0 then @.a= linein(f); return
/*──────────────────────────────────────────────────────────────────────────────────────*/
srt: procedure expose sWork; parse arg #
do j=1 for #; fn= sWORK || j; 'SORT' fn "/O" fn; end /*j*/; return</lang>
<br><br>
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