Calculate and Decrease Array Values

Question

Calculate and Decrease Array Values

Asked 6 years, 8 months ago

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1

I am trying to decrement and calculate values of an array unsuccessfully. The decrementation works to a certain extent, so it decreases different values than what is clicked on the checkbox and the calculation appears on the console as Nan.

orders = [
{id_service: "1", id_empresa: "9", nome_service: "Servico 01", qtd: "0", checkup: "false", price_service : "250"},

{id_service: "2", id_empresa: "9", nome_service: "Servico 02", qtd: "0", checkup: "false" price_service : "300"},

{id_service: "3", id_empresa: "9", nome_service: "Servico 03", qtd: "0", checkup: "false" price_service : "400"}
]

calc(i) {
  let obj = JSON.parse(this.orders[i].price_service);


  if (this.orders[i].qtd == 0) {
    this.result.push(obj);
    this.orders[i].qtd = 1;
  }
  else {
    this.result.splice(i, 1);
    this.orders[i].qtd = 0;
  }
  this.result.reduce(function (a, b) {
    return a + b['obj'];
  }, 0);
  
}

<div *ngFor="let item of orders; let i = index; ">
    <ion-item>
      <ion-label class="title">{{item.nome_service}}
        <span>{{item.price_service}}</span>
      </ion-label>
      <ion-checkbox (click)="calc(i)" checked="{{item.checkup}}" color="green"></ion-checkbox>
    </ion-item>
    <p>{{result}}</p>
  </div>

I did not understand where you are decreasing the value in the code, I could understand that you are only setting "0" or "1", can explain better?

– Ricardo Pontual

2018/03/19 at 11:25
@Ricardopunctual I’m decreasing with splice function within LSE

– Henrique Mendes Silveira Rodri

2018/03/19 at 12:16
I saw this line, so you are removing items from the array. This will not work because, when you run Binding from angular, the indices shall be sequential, i.e.: 1,2,3 or 0,1,2 depending on index, and you pass this index to Function in the click with the calc(i). If you click the first item for example, it will remove element 1, so element 2 becomes the first. What will happen when you click on element 2? The second element will be removed, which is now item 3! Try to pass the id_servicefor Function calc to remove the correct element.

– Ricardo Pontual

2018/03/19 at 13:05

1 answer

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by NoobSaibot • **9,554** points · Answer 1 · 2018-03-20T07:50:18+00:00

Since the intention is to add up the value of price_service of all items containing the property qtd equal to 1, there is no need to create a new object. Just filter the object orders using the method filter and recover all items containing the property qtd equal to 1, then use the method reduce.

I took the liberty of making some modifications, to facilitate, I removed all double quotes from properties that are number and boolean.

orders = [
  { id_service: 1, id_empresa: 9, nome_service: "Servico 01", qtd: 0, checkup: false, price_service: 250 },
  { id_service: 2, id_empresa: 9, nome_service: "Servico 02", qtd: 0, checkup: false, price_service: 300 },
  { id_service: 3, id_empresa: 9, nome_service: "Servico 03", qtd: 0, checkup: false, price_service: 400 }
];

Create a variable to store the sum value:

total: number = 0;

His method calc was like this:

calc(i) {
  this.orders[i].qtd = (this.orders[i].qtd === 0) ? 1 : 0;
  this.total = this.orders.filter(item => item.qtd === 1).reduce((a, b) => a + b.price_service, 0);
  console.log(this.total);
}

Explanation

When performing this.orders.filter(item => item.qtd === 1) a new array is returned with the elements that passed the test implemented by the given method, which in this case is: item => item.qtd === 1.

In the method reduce the sum of the value of a with the value of the property price_service of the element b.

You can see running on stackblitz