如何在比较另一个对象的同时过滤对象数组？

Question

I'm trying to search through a list of cars (which have a make, model, price, and other values) and compare it to the car I am searching for on my form.

I know how to do it where I compare the two cars exactly, but I'm not sure how to filter it when I, for example, only want to search by make and show all the cars by the same make (but not worry about the other values since nothing else was selected).

I've tried using the lowdash ._isEqual() , which worked if the two objects are exactly the same. But, I have no idea how to do it if I only want to search by a certain make, or only a certain year, or something like that.

app.component.ts

export class AppComponent {
  cars:Car[];
  title = 'car-dealership';

  constructor(private carsService:CarsService) {}

  searchCars(car:Car) {
    this.carsService.getAllCars().subscribe(resp => {
      this.cars = resp;
      this.cars.filter(c => {
        //do something
      })
    })
  }
}

input-form.component.ts

export class InputFormComponent implements OnInit {
  @Output() searchCars: EventEmitter<any> = new EventEmitter();

  make:string;
  year:number;
  color:string;
  sunRoof = false;
  fourWheel = false;
  lowMiles = false;
  powerWindows = false;
  navigation = false;
  heatedSeats = false;
  price:number;

  constructor() { }

  ngOnInit() {
  }

  onSubmit() {
    const selectedCar = {
      color: this.color,
      hasHeatedSeats: this.heatedSeats,
      hasLowMiles: this.lowMiles,
      hasNavigation: this.navigation,
      hasPowerWindows: this.powerWindows,
      hasSunroof: this.sunRoof,
      isFourWheelDrive: this.fourWheel,
      make: this.make,
      price: Number(this.price),
      year: Number(this.year)
    }
    console.log('form submitted with:', selectedCar);
    this.searchCars.emit(selectedCar);
  } 
}

cars.service.ts

export class CarsService {

  constructor() {}

  getAllCars() {
    return of(Cars);
  }
}

Answer 1

The filter method just needs to return if the item should be included - if it returns true (or any other "truthy" value) the item is included, and excluded otherwise.

  searchCars(car:Car) {
    this.carsService.getAllCars().subscribe(resp => {
      this.cars = resp.filter(c => {
        return c.make === this.make; // Or whatever complicated logic you want to use
      });
    });
  }

---

From your comment, I understand that you need to check two things: 1) should this criteria be used and 2) does the item match the criteria.

So, let's code that!

  searchCars(car:Car) {
    this.carsService.getAllCars().subscribe(resp => {
      this.cars = resp.filter(c => {
        // First, check if the criteria should be used
        if (this.make && this.make.length > 0) {
          return c.make === this.make;
        }
        // Return a default value if the criteria isn't being used
        return true;
      });
    });
  }

Ok, that's great. But what if it needs to match zero, one, or TWO conditions?

Well, we're going to use a "trick" or "pattern" called the "early return". Instead of checking that it matches ALL conditions and returning true, we'll check if it doesn't match EACH condition and return false:

  searchCars(car:Car) {
    this.carsService.getAllCars().subscribe(resp => {
      this.cars = resp.filter(c => {
        // First, check if the criteria should be used
        if (this.make && this.make.length > 0) {
          // Then, check if it doesn't match
          if (c.make !== this.make) {
            // Early return, it doesn't matter what the other checks say
            // we know this shouldn't be included.
            return false;
          }
        }
        // First, check if the criteria should be used
        if (this.color && this.color.length > 0) {
          // Then, check if it doesn't match
          if (c.color !== this.color) {
            // Early return, it doesn't matter what the other checks say
            // we know this shouldn't be included.
            return false;
          }
        }
        // Repeat for all conditions you need to look at

        // Return a default value. If the code gets here it means either:
        // 1) no conditions are applied
        // 2) it matches all relevant conditions
        return true;
      });
    });
  }

Answer 2

Try the below

this.cars.filter(c => {
        return c.make == this.make // You can have multiple conditions here
})

Filter method returns items in a new array which satisfies the condition.

Answer 3

You only need to tell filter function what condition you want to check in your array, and it will return each element your condition become true, for example, if you want to filter by make:

this.cars.filter(c => {
    c.make === 'SOME_MAKE'
});

You can also add multiple filters:

this.cars.filter(c => {
    c.make === 'SOME_MAKE' && c.year === 2015  // Filtering by make and year
});