Javascript how to sort by dynamic property

Question

I have the following array, and I want to sort it following these rules

Primary true and shouldPrioritize true
Primary true and shouldPrioritize false
Primary false and shouldPrioritize true
Primary false and shouldPrioritize false

const array = [{
  primary: true
  shouldPrioritize: false,
},
{
  primary: true
  shouldPrioritize: true,
}
{
  primary: false
  shouldPrioritize: true,
}
{
  primary: false
  shouldPrioritize: false,
}
]

What's the easiest way of using sort to match the rules? If we remove one of the items we should sort accordingly too.

Nina Scholz · Accepted Answer · 2021-01-22 16:18:22Z

2

Just take the deltas of the booleans.

const
    array = [{ primary: true, shouldPrioritize: false }, { primary: true, shouldPrioritize: true }, { primary: false, shouldPrioritize: true }, { primary: false, shouldPrioritize: false }];
    
array.sort((a, b) => b.primary - a.primary || b.shouldPrioritize - a.shouldPrioritize);

console.log(array);

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answered Jan 22, 2021 at 16:18

Nina Scholz

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2 Comments

RFFD Over a year ago

Thank you! That worked. I'm just using TypeScript, which throws the following error. ``` The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type. ``` Is there an easy workaround for that?

Nina Scholz Over a year ago

@RFFD, sorry i have no idea of typescript.

Lennholm · Accepted Answer · 2021-01-22 16:28:13Z

The easiest way to sort is to use the array's native sort() method. It takes a function that compares two items in the array and returns a number. If the function returns a negative number, the first item is placed before the second item but if it returns a positive number they get reversed.

In your case, you can do this by considering your boolean values as numbers. In JS, booleans can be implicitly coerced into numbers, true to 1 and false to 0. According to your rules, the primary property has a higher precedent than shouldPrioritize, so lets's increase its value by one. Then it's only a matter of sorting by the principle put higher values first.

Your solution can then look like this:

const array = [{ primary: true, shouldPrioritize: false }, { primary: true, shouldPrioritize: true }, { primary: false, shouldPrioritize: true }, { primary: false, shouldPrioritize: false }];

array.sort((a, b) => (b.primary * 2 + b.shouldPrioritize) - (a.primary * 2 + a.shouldPrioritize));

console.log(array);

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