Discussed: Tiny modules — Hate of pyramids — Permutations — Simons age and taste in beverages
So, yesterday I published a small ~53 LOC npm module called permuter on Github. Permuter is a small utility for doing permutations between objects and applying rules to the generated permutations.
It was all triggered by this pyramid of nested for loops/if statements:
// Apply mixins
if (r.metadata.mixin) {
for (range in r.metadata.mixin) {
for (version in report.services[r.service]) {
if (lib.semver.satisfies(version, range)) {
for (attribute in r.metadata.mixin[range]) {
report.services[r.service][version][attribute] = r.metadata.mixin[range][attribute];
}
}
}
}
}
I always hate when I have to choose between long ass object-walking report.services[r.service][version][attribute] or adding lots of temporary reference variables into the scope. So these ten lines of code annoyed me, and thus permuter was born, and allowed me to do this:
lib.permuter(
"mixins", r.metadata.mixin,
report.services[r.service],
function satisfiesRange(mixin, service) {
return lib.semver.satisfies(service.key, mixin.key);
},
"$mixins",
function permutation(mixin, service, attribute) {
service.value[attribute.key] = attribute.value;
});
This doesn't really cut it as an introductory example to permuter, but kind of illustrates how it can be used to solve some problems a teensy bit more elegantly.
A simple example
permuter(
["a", "b"],
[1, 2],
function(letter, number) {
console.log(letter.value, number.value);
}
)
This produces the following output:
a 1
a 2
b 1
b 2
A slightly more advanced example
Here's a slightly more advanced example where we add a blocker function applySomeReasoning that only accepts permutations where the xFactor is twice the size of Number. WE also use a backreference to iterate over the letters of the selected word.
permuter(
[1, 2, 5, 10], // Number
[10, 4], // xFactor
function applySomeReasoning(number, xFactor) {
return number.value*2 == xFactor.value;
},
"words", ["a", "bo"],
"$words", // Letter
function(number, xFactor, word, letter) {
console.log(word.value, letter.value, number.value, xFactor.value);
}
)
The result of this is:
a a 2 4
bo b 2 4
bo o 2 4
a a 5 10
bo b 5 10
bo o 5 10
A more convoluted example
Here is a more convoluted and silly example where backreferences and block functions also are used. Backreferences are used to include the value of a previously selected item in the permutation set. In the example below we will include ["Cola", "Tonic"] when "beverage" is selected and ["Snickers", "Chips"] when "snack" is selected. Blocker functions are used to exclude certain permutations, if "Simon" is too young to see the movie "Splatter" we'll stop those combinations in checkAgeLimit, likewise we don't force people to eat or drink what they really dislike by adding the blocker checkIntenseDislikes.
var lib = {
permuter: require('permuter')
}
var people = {
"Hugo": {"age":31},
"Simon": {"age":24, "dislikes":"Tonic"},
}
var snacks = {
"beverage": {
"Cola": {"effect":"refreshed", "leftover":"mug"},
"Tonic": {"effect":"happy", "leftover":"bottle"}
},
"snack": {
"Snickers": {"effect":"sticky", "leftover":"wrapper"},
"Chips": {"effect":"thirsty", "leftover":"bag"}
}
}
var salons = {
"Salon 1": {"movie": "Slasher", "ageLimit": 30},
"Salon 2": {"movie": "Kidpix", "ageLimit": 10}
}
lib.permuter(
people,
"snackType", snacks,
salons,
function checkAgeLimit(person, snackType, salon) {
return person.value.age >= salon.value.ageLimit;
},
"$snackType",
function checkIntenseDislikes(person, snackType, salon, snack) {
return !person.value.dislikes || person.value.dislikes != snack.key;
},
function permutationResult(person, snackType, salon, snack) {
var snackName = snack.key, salonName = salon.key;
salon = salon.value, snack = snack.value;
salon.trash = salon.trash || {};
salon.trash[snack.leftover] = salon.trash[snack.leftover] ?
salon.trash[snack.leftover] + 1 : 1;
console.log(person.key, "goes to", salonName ,"and sees", salon.movie, "and consume the tasty", snackType.key, snackName,
"and will then feel", snack.effect, "and leave a", snack.leftover, "on the floor");
}
);
console.log("\nAfter a long day the staff collects the following from the floor");
lib.permuter(salons, function(salon) {
var trash;
console.log(salon.key + ":");
for (trash in salon.value.trash) {
console.log('\t', trash+':', salon.value.trash[trash]);
}
})
The output from this is:
Hugo goes to Salon 1 and sees Slasher and consume the tasty beverage Cola and will then feel refreshed and leave a mug on the floor
Hugo goes to Salon 1 and sees Slasher and consume the tasty beverage Tonic and will then feel happy and leave a bottle on the floor
Hugo goes to Salon 2 and sees Kidpix and consume the tasty beverage Cola and will then feel refreshed and leave a mug on the floor
Hugo goes to Salon 2 and sees Kidpix and consume the tasty beverage Tonic and will then feel happy and leave a bottle on the floor
Hugo goes to Salon 1 and sees Slasher and consume the tasty snack Snickers and will then feel sticky and leave a wrapper on the floor
Hugo goes to Salon 1 and sees Slasher and consume the tasty snack Chips and will then feel thirsty and leave a bag on the floor
Hugo goes to Salon 2 and sees Kidpix and consume the tasty snack Snickers and will then feel sticky and leave a wrapper on the floor
Hugo goes to Salon 2 and sees Kidpix and consume the tasty snack Chips and will then feel thirsty and leave a bag on the floor
Simon goes to Salon 2 and sees Kidpix and consume the tasty beverage Cola and will then feel refreshed and leave a mug on the floor
Simon goes to Salon 2 and sees Kidpix and consume the tasty snack Snickers and will then feel sticky and leave a wrapper on the floor
Simon goes to Salon 2 and sees Kidpix and consume the tasty snack Chips and will then feel thirsty and leave a bag on the floor
After a long day the staff collects the following from the floor
Salon 1:
mug: 1
bottle: 1
wrapper: 1
bag: 1
Salon 2:
mug: 2
bottle: 1
wrapper: 2
bag: 2
The permuter call with the main data set replaces the following loop:
var firstname, person, snackType, snackList, salonName, salon,
snackName, snack;
for (firstname in people) {
person = people[firstname];
for (snackType in snacks) {
snackList = snacks[snackType];
for (salonName in salons) {
salon = salons[salonName];
if (person.age >= salon.ageLimit) {
for (snackName in snackList) {
snack = snackList[snackName];
if (!person.dislikes || person.dislikes !== snackName) {
salon.trash = salon.trash || {};
salon.trash[snack.leftover] = salon.trash[snack.leftover] ?
salon.trash[snack.leftover] + 1 : 1;
console.log(firstname, "goes to", salonName ,"and sees", salon.movie, "and consume the tasty", snackType, snackName,
"and will then feel", snack.effect, "and leave a", snack.leftover, "on the floor");
}
}
}
}
}
}