Filter by multiple array conditions

Question

The filter method is a really powerful tool for filtering by single or multiple conditions, but is there a way to filter by conditions of arrays?

class Car with properties : model, color, engineStatus.

• cars is an array with few cars

By one condition would look like:

let currModel = `Opel`

let filterdObject = cars.filter { $0.model == currModel }

By two or more conditions would look like:

let currModel = `Opel`
let currColor = `Green`

let filterdObject = cars.filter { $0.model == currModel || $0.color == currColor }

My question is it how could I filter by an array like:

An array has ,e.g., two colors blue and green. I would like to filter cars by these colors. My point is to get a formula for n-conditions.

Answer 1

Forget about the filter for a moment. Think how you would check if a car's color is a value in an array.

let colors = [ "Green", "Blue" ]
// or let colors: Set = [ "Green", "Blue" ]
if colors.contains(someCar.color) {
}

Simple enough. Now use that same simple expression in the filter.

let filterdObject = cars.filter { $0.model == currModel || colors.contains($0.color) }

Answer 2

Treat the filter closures like a value type and store them in an array. Use the inner reduce call to create a single boolean value that is true is all of the conditions are met by the current car. If you need a compound test like color == "blue" or "green" then simply add that to your filter closure conditions array.

    struct Car {
      let model: String
      let color: String
    }

    let conditions: [(Car) -> Bool] = [
      {$0.model == "Opel"},
      {$0.color == "Red"},
    ]

    let carLot = [
      Car(model: "Opel", color: "Green"),
      Car(model: "Mustang", color: "Gold"),
      Car(model: "Opel", color: "Red"),
    ]

    let allRedOpels = carLot.filter {
      car in
      conditions.reduce(true) { $0 && $1(car) }
   }