Hash join: Difference between revisions

=={{header|Tcl}}==

<lang tcl>package require Tcl 8.6

proc joinTables {tableA indexA tableB indexB} {

# Optimisation: if the first table is longer, do in reverse order

if {[llength $tableB] < [llength $tableA]} {

return [lmap pair [joinTables $tableB $indexB $tableA $indexA] {

lreverse $pair

}]

}

foreach value $tableA {

set hashmap([lindex $value $indexA]) $value

}

lmap value $tableB {

set key [lindex $value $indexB]

if {![info exist hashmap($key)]} continue

list $hashmap($key) $value

}

}

set tableA {

{27 "Jonah"} {18 "Alan"} {28 "Glory"} {18 "Popeye"} {28 "Alan"}

}

set tableB {

{"Jonah" "Whales"} {"Jonah" "Spiders"} {"Alan" "Ghosts"} {"Alan" "Zombies"}

{"Glory" "Buffy"}

}

set joined [joinTables $tableA 1 $tableB 0]

foreach row $joined {

puts $row

}</lang>

{{out}}

<pre>

{27 "Jonah"} {"Jonah" "Whales"}

{27 "Jonah"} {"Jonah" "Spiders"}

{28 "Alan"} {"Alan" "Ghosts"}

{28 "Alan"} {"Alan" "Zombies"}

{28 "Glory"} {"Glory" "Buffy"}

</pre>