Hash join: Difference between revisions

=={{header|JavaScript}}==

===ES6===

<lang JavaScript>(() => {

'use strict';

// hashJoin :: [Dict] -> [Dict] -> String -> [Dict]

let hashJoin = (tblA, tblB, strJoin) => {

let [jA, jB] = strJoin.split('='),

M = tblB.reduce((a, x) => {

let id = x[jB];

return (

a[id] ? a[id].push(x) : a[id] = [x],

a

);

}, {});

return tblA.reduce((a, x) => {

let match = M[x[jA]];

return match ? (

a.concat(match.map(row => dictConcat(x, row)))

) : a;

}, []);

},

// dictConcat :: Dict -> Dict -> Dict

dictConcat = (dctA, dctB) => {

let ok = Object.keys;

return ok(dctB).reduce(

(a, k) => (a['B_' + k] = dctB[k]) && a,

ok(dctA).reduce(

(a, k) => (a['A_' + k] = dctA[k]) && a, {}

)

);

};

// TEST

let lstA = [

{ age: 27, name: 'Jonah' },

{ age: 18, name: 'Alan' },

{ age: 28, name: 'Glory' },

{ age: 18, name: 'Popeye' },

{ age: 28, name: 'Alan' }

],

lstB = [

{ character: 'Jonah', nemesis: 'Whales' },

{ character: 'Jonah', nemesis: 'Spiders' },

{ character: 'Alan', nemesis: 'Ghosts' },

{ character:'Alan', nemesis: 'Zombies' },

{ character: 'Glory', nemesis: 'Buffy' },

{ character: 'Bob', nemesis: 'foo' }

];

return hashJoin(lstA, lstB, 'name=character');

})();

</lang>

{{Out}}

<pre>[{"A_age":27,"A_name":"Jonah","B_character":"Jonah","B_nemesis":"Whales"},

{"A_age":27,"A_name":"Jonah","B_character":"Jonah","B_nemesis":"Spiders"},

{"A_age":18,"A_name":"Alan","B_character":"Alan","B_nemesis":"Ghosts"},

{"A_age":18,"A_name":"Alan","B_character":"Alan","B_nemesis":"Zombies"},

{"A_age":28,"A_name":"Glory","B_character":"Glory","B_nemesis":"Buffy"},

{"A_age":28,"A_name":"Alan","B_character":"Alan","B_nemesis":"Ghosts"},

{"A_age":28,"A_name":"Alan","B_character":"Alan","B_nemesis":"Zombies"}]</pre>