Scalable sorting system by parameters

Question

How to write a system for sorting data by parameters so that it scales well regardless of the number of various parameters? For example, there is a conditional json-format in which data is stored:

{ "city": "Москва", "population": "12", "standart_of_living": "9.5", "per_capita_income": "50000", "trust_in_government": "9.8" }

If you write code in JavaScript, you get a static loop without the ability to dynamically add / remove parameters. And if I wrote a simple static sample, I would do this:

 for(let i = 0; i < json.length; i++) { if(json[i].population >= 10 && json[i].standart_of_living >= 8) $('#some_div').append("Город: " + json[i].city); }

The result of the cycle would be the conclusion Город: Москва . But what if the user on the page wants to choose cities by the parameter "Trust level in government" (trust_in_government)? My code is static and I cannot dynamically add the && json[i].trust_in_government >= 9 parameter to it. Is there an algorithm that allows sorting by parameters without having to scribble through mountains of code?

Accepted Answer · 2017-06-06T10:16:54

There is a filter method that allows you to reduce the code you write to a single line:

 json.filter(i => i.population>9 && i.standart_of_living>7).forEach(i => $('#some_div').append(`Город: ${i.city}`));

Using the composition and the every method, it is easy to use it to filter by any parameters:

 let rules = [ {prop: 'population', val: 9}, {prop: 'standart_of_living', val: 7}, ]; json.filter(i => rules.every(rule => i[rule.prop]>rule.val))

The only problem is that you cannot put a comparison operator in the array of rules. But you can put it there as a string, and use it with an eval , a Function constructor, or a trivial switch, like this:

 let rules = [ {prop: 'population', val: 9, op: '=='}, {prop: 'standart_of_living', val: 7, op: '>'}, ]; // Вариант с eval самый короткий, если бы я делал не для примера, я бы использовал switch: json.filter(i => rules.every(rule => eval(`${i[rule.prop]}${rule.op}${rule.val}`)))

Now, instead of scribbling mountains of code, for each new filtering rule you need to add three parameters to the array of rules - what to compare, how to compare, what to compare with.

 const json = [ {a:1, b:2, c: 'Test'}, {a:1, b:20, c: 'Hello world'}, {a:1, b:-2, c: 'Test'}, {a:1, b:'2', c: 'Hello world'}, {a:'Hello world', c: 'Test'}, {a:1, b:[], c: 'Test'} ]; // Вариант с switch: const filter = rules => json.filter(i => rules.every(rule => { switch (rule.op){ case "===": return i[rule.prop] === rule.val; case "==": return i[rule.prop] == rule.val; case "!=": return i[rule.prop] != rule.val; case "!==": return i[rule.prop] !== rule.val; case ">": return i[rule.prop] > rule.val; case "<": return i[rule.prop] < rule.val; case "<=": return i[rule.prop] <= rule.val; case ">=": return i[rule.prop] >= rule.val; default: return false; } })); console.log(filter([{prop: 'a', val: 1, op: '!='}])); console.log(filter([{prop: 'b', val: 0, op: '>'}])); console.log(filter([{prop: 'b', val: undefined, op: '==='}]));

That is, to add a new rule, I can, for example, bind to the checkbox.
And when the checkbox is checked, call the push() method and insert a new rule into the array of rules?
You can modify this algorithm for training so that it checks the nested fields)
Over time, the logic in my application changed and the arrays became objects.
Now I have both rules - an object, and json - an object.
Could you describe the application logic so that I can rewrite the algorithm myself?
Now I understand that it works like this - there are two cycles, one is nested in the other (every nested in filter).
In switch checked if the operation matches what is specified in rule.op and returns a boolean value.
If true, then the json array element is pushed into a temporary array.

Scalable sorting system by parameters

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