在数组中查找唯一属性并计算匹配项

Question

I want to find matching items in this array using the property category , in this app each user can have custom categories so the server cannot know the name of categories prior to running the function.

0: {amount: "123", category: "drinks", location: "NYC", note: "piano bar", receipt: "img.jpg", …}
1: {amount: "123", category: "drinks", location: "NYC", note: "piano bar", receipt: "img.jpg", …}
2: {amount: "123", category: "bills", location: "NYC", note: "piano bar", receipt: "img.jpg", …}
3: {amount: "123", category: "savings", location: "NYC", note: "piano bar", receipt: "img.jpg, ...}

This my code so far

fetch = () => {
    this.setState({ loading: true });
    const { currentUser } = fire.auth();
    var stamp = moment().format('LLLL');
    const wallet = fire.database().ref(`/master/${currentUser.uid}/wallets/cash/income/transactions/20190520`);
    wallet.on('value', snapshot => {
      var data = snapshot.val();
      var categories = []
      for (let i in data) {
        categories.push(data[i].category)
      };
      console.log(categories);
      this.setState({ loading: false, ok: true });
    })
  }

Here my goal is find all categories in this array and store them in value like {drinks,bills,savings} and then see how many items match this category like

• drinks 2
• bills 1
• savings 1

Answer 1

You could use reduce to get all categories with a count of the number of array elements associated with each one.

 const arr = [{ amount: "123", category: "drinks", location: "NYC", note: "piano bar", receipt: "img.jpg" }, { amount: "123", category: "drinks", location: "NYC", note: "piano bar", receipt: "img.jpg" }, { amount: "123", category: "bills", location: "NYC", note: "piano bar", receipt: "img.jpg" }, { amount: "123", category: "savings", location: "NYC", note: "piano bar", receipt: "img.jpg" }]; const categories = arr.reduce((acc, obj) => { const category = obj.category; if (category in acc) { acc[category] += 1; } else { acc[category] = 1; } return acc; }, {}); console.log(categories); // { drinks: 2, bills: 1, savings: 1 }

Answer 2

you can use Es6 Map class to store key as category and value as array of matching element. Map provides plenty of methods as well that you can check here

let yourArray = [{
        amount: "123",
        category: "drinks",
        location: "NYC",
        note: "piano bar",
        receipt: "img.jpg"
    },
    {
        amount: "123",
        category: "drinks",
        location: "NYC",
        note: "piano bar",
        receipt: "img.jpg"
    },
    {
        amount: "123",
        category: "bills",
        location: "NYC",
        note: "piano bar",
        receipt: "img.jpg"
    },
    {
        amount: "123",
        category: "savings",
        location: "NYC",
        note: "piano bar",
        receipt: "img.jpg"
    }
]


var newMap = new Map();


yourArray.forEach(ele => {
    if (!newMap.get(ele.category)) {
        newMap.set(ele.category, [ele])
    } else {
        newMap.get(ele.category).push(ele)
    }
})

console.log(newMap)
newMap.forEach((value, key) => {
    console.log(`${key} ${value.length}`)
})

Answer 3

you can try using the for each loop and iterate over them and save the count in an object

    let data = [
{amount: "123", category: "drinks", location: "NYC", note: "piano bar", receipt: "img.jpg"},
{amount: "123", category: "drinks", location: "NYC", note: "piano bar", receipt: "img.jpg"},
{amount: "123", category: "bills", location: "NYC", note: "piano bar", receipt: "img.jpg"},
{amount: "123", category: "savings", location: "NYC", note: "piano bar", receipt: "img.jpg"}];

let countObj = {};
data.forEach((val,ind)=>{
    if(countObj[val.category]){
        countObj[val.category] = countObj[val.category] + 1 ;
  }else{
    countObj[val.category] = 1;
  }
})
console.log(countObj);

gives the result

bills: 1
drinks: 2
savings: 1

Answer 4

You could use array.includes to see if your value already exists, and count the amount in another array like this:

 fetch = () => {
        this.setState({ loading: true });
        const { currentUser } = fire.auth();
        var stamp = moment().format('LLLL');
        const wallet = fire.database().ref(`/master/${currentUser.uid}/wallets/cash/income/transactions/20190520`);
        wallet.on('value', snapshot => {
          var data = snapshot.val();
          var categories = [];
          var amounts = [];
          for (let i in data) {
            if(categories.includes(data[i].category){
                if(amounts[data[i].category] == undefined){
                   amounts[data[i].category]=1;
                }else{
                   amounts[data[i].category]++;
                }
            }
            categories.push(data[i].category)
          };
          console.log(amounts);
          this.setState({ loading: false, ok: true });
        })
      }