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September 28, 2018 07:43
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javascript cartesian product using generator functions (streaming)
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/* | |
streaming cartesian product elements uses less memory ... | |
*/ | |
const generator = cartesianProductSimplified(['a', 'b'], [1, 2, 3, 4], ['x', 'y', 'z']); | |
/* prints | |
[ 'a', 1, 'x' ] | |
[ 'a', 1, 'y' ] | |
[ 'a', 1, 'z' ] | |
[ 'a', 2, 'x' ] | |
[ 'a', 2, 'y' ] | |
[ 'a', 2, 'z' ] | |
[ 'a', 3, 'x' ] | |
[ 'a', 3, 'y' ] | |
[ 'a', 3, 'z' ] | |
[ 'a', 4, 'x' ] | |
[ 'a', 4, 'y' ] | |
[ 'a', 4, 'z' ] | |
[ 'b', 1, 'x' ] | |
[ 'b', 1, 'y' ] | |
[ 'b', 1, 'z' ] | |
[ 'b', 2, 'x' ] | |
[ 'b', 2, 'y' ] | |
[ 'b', 2, 'z' ] | |
[ 'b', 3, 'x' ] | |
[ 'b', 3, 'y' ] | |
[ 'b', 3, 'z' ] | |
[ 'b', 4, 'x' ] | |
[ 'b', 4, 'y' ] | |
[ 'b', 4, 'z' ] | |
*/ | |
printValues(generator); | |
// helper function to print all values from a generator function | |
function printValues(generator) { | |
let iteration = null; | |
while (iteration = generator.next()) { | |
if (iteration.done === true) { | |
break; | |
} | |
console.log(iteration.value); | |
} | |
} | |
// helper function to construct the arguments array for the 'cartesianProduct' class | |
function cartesianProductSimplified(...arrays) { | |
let args = []; | |
for (let i = 1; i < arrays.length; i++) { | |
args = args.concat([cartesianProduct, arrays[i]]); | |
} | |
args.splice(0, 0, arrays[0]); | |
return cartesianProduct(...args); | |
} | |
/* | |
call it like this: | |
cartesianProduct(['a', 'b'], cartesianProduct, [1, 2, 3, 4], cartesianProduct, ['x', 'y', 'z']); | |
use cartesianProductSimplified to simplify it: | |
cartesianProductSimplified(['a', 'b'], [1, 2, 3, 4], ['x', 'y', 'z']) | |
*/ | |
function* cartesianProduct(values, generator, ...generatorArgs) { | |
for (const value of values) { | |
if (generator) { | |
const iterator = generator(...generatorArgs); | |
let iteration = null; | |
while (iteration = iterator.next()) { | |
if (iteration.done === true) { | |
break; | |
} | |
yield [value, ...iteration.value]; | |
} | |
} else { | |
yield [value]; | |
} | |
} | |
} |
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