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.

Something like cars.filter {arrayOfColors(contains:$0.color)}? — Larme
– Larme, Commented Apr 11, 2017 at 14:11
@Larme would looks like` cars.filter {arrayOfColors.contains($0.color)}` - new syntax — yerpy
– yerpy, Commented Apr 11, 2017 at 14:16
I don't use Swift, when I comment on Swift, it's just pointing out what could possibly a way to go, code not assured at all to compile, but understandable. But thanks to correct (in case of someone taking "as such" the indication). — Larme
– Larme, Commented Apr 11, 2017 at 14:18

rmaddy · Accepted Answer · 2017-04-11 14:18:24Z

60

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) }

edited Apr 11, 2017 at 14:18

answered Apr 11, 2017 at 14:11

rmaddy

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2 Comments

Alladinian Over a year ago

I don't get the downvote either, this is a valid solution... Having said that, a membership test against a Set instead of an Array could be more suitable here.

rmaddy Over a year ago

@Alladinian Good suggestion on the use of Set. The OP mentioned having an array.

Price Ringo · Accepted Answer · 2017-04-11 15:05:46Z

10

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) }
   }

edited Apr 11, 2017 at 15:05

answered Apr 11, 2017 at 14:24

Price Ringo

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2 Comments

Alexander Over a year ago

That reduce approach isn't so good because it doesn't perform any short circuiting

Matthijs Over a year ago

Thank you very much for this, it saved my day and a lot of work!

gflo · Accepted Answer · 2023-08-31 16:39:55Z

2

To piggy-back off Price Ringo's answer you could use allSatisfy instead of reduce to get a cleaner read of the code:

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.allSatisfy { $0(car) }
}

answered Aug 31, 2023 at 16:39

gflo

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