Hash join: Difference between revisions

Line 989:

<pre>$ txr hash-join.txr

(((27 Jonah) (Jonah Whales)) ((27 Jonah) (Jonah Spiders)) ((18 Alan) (Alan Ghosts)) ((28 Alan) (Alan Ghosts)) ((18 Alan) (Alan Zombies)) ((28 Alan) (Alan Zombies)) ((28 Glory) (Glory Buffy)))</pre>

=={{header|zkl}}==

Join two tables by hashing on the common key (name). The resulting join is the intersection of the two tables.

<lang zkl>ageName:=T(27,"Jonah", 18,"Alan", 28,"Glory", 18,"Popeye", 28,"Alan");

nameNemesis:=T("Jonah","Whales", "Jonah","Spiders", "Alan","Ghosts",

"Alan","Zombies", "Glory","Buffy");

fcn addAN(age,name,d){ // keys are names, values are ( (age,...),() )

if (r:=d.find(name)) d[name] = T(r[0].append(age),r[1]);

else d.add(name,T(T(age),T));

d // return d so pump will use that as result for assignment

}

fcn addNN(name,nemesis,d){ // values-->( (age,age...), (nemesis,...) )

if (r:=d.find(name)){

ages,nemesises := r;

d[name] = T(ages,nemesises.append(nemesis));

}

// (Void.Read,1) --> take existing i, read next one, pass both to next function

var d=ageName.pump(Void,T.fp(Void.Read,1),T(addAN,Dictionary()));

nameNemesis.pump(Void,T.fp(Void.Read,1),T(addNN,d));

d.println(); // the union of the two tables

d.keys.sort().pump(Console.println,'wrap(name){ //pretty print the join

val:=d[name]; if (not val[1])return(Void.Skip);

String(name,":",d[name][1].concat(","));

})

</lang>

zkl Dictionaries only have one key

<pre>

D(Popeye:L(L(18),L()),Glory:L(L(28),L("Buffy")),

Jonah:L(L(27),L("Whales","Spiders")),Alan:L(L(18,28),L("Ghosts","Zombies")))

Alan:Ghosts,Zombies

Glory:Buffy

Jonah:Whales,Spiders

</pre>