Update array object values based on another array items

Question

I have this lst, which has the name and total available.

let lst = [
 { name: 'Apple', total: 4 },
 { name: 'Mango', total: 9 },
 { name: 'Orange', total: 6 },
 { name: 'Passion', total: 2 }
]

Now there is a new list json which I receive from an api, that only has names of the items, I changed to an array like this.

let newlst = ["Apple","Orange","Banana","Mango","Apple","Pineapple","Passion"]

So how do I go on about for each item in newlst that is found in lst array then sum their total +1 .... If not then skip.

So expected out is

let lst = [
 { name: 'Apple', total: 6 },
 { name: 'Mango', total: 10 },
 { name: 'Orange', total: 7 },
 { name: 'Passion', total: 3 }
]

Answer 1

you can do it by loop also. compare the array elements and json object name and than increase the total of that corresponding json object.

let lst = [
 { name: 'Apple', total: 4 },
 { name: 'Mango', total: 9 },
 { name: 'Orange', total: 6 },
 { name: 'Passion', total: 2 }
];
let newlst = ["Apple","Orange","Banana","Mango","Apple","Pineapple","Passion"];
for(i=0;i<lst.length;i++){
 for(j=0;j<newlst.length;j++){
 if(lst[i].name === newlst[j]){
 lst[i].total++;
 } 
 }
 }
 console.log(lst)

Answer 2

You can loop through the lst and update the total by counting the fruits in the newlst using filter()

let lst = [
 { name: 'Apple', total: 4 },
 { name: 'Mango', total: 9 },
 { name: 'Orange', total: 6 },
 { name: 'Passion', total: 2 }
];
let newlst = ["Apple","Orange","Banana","Mango","Apple","Pineapple","Passion"];
lst.forEach(function(fruit){
 //get the count in newlst
 let count = newlst.filter(f => f == fruit.name).length;
 //update the total by adding
 fruit.total = fruit.total + count;
});
console.log(lst);

• Vulwsztyn: why forEach not map? why == instead of ===?
• Mamun: @Vulwsztyn, not any particular reason. I thought this could be easier for OP to understand:)
• Som Shekhar Mukherjee: For every item in lst you again and again filter newlst, which is an O(N*M) solution. It could have been more efficient.

Answer 3

Why do you use let instead of const? you shouldn't You could do it like this

lst.map(({ name, total }) => ({ name, total: total + newlst.filter((x) => x === name).length }))

const lst = [
 { name: 'Apple', total: 4 },
 { name: 'Mango', total: 9 },
 { name: 'Orange', total: 6 },
 { name: 'Passion', total: 2 }
]
const newlst = ["Apple","Orange","Banana","Mango","Apple","Pineapple","Passion"]
console.log(lst.map(({ name, total }) => ({ name, total: total + newlst.filter((x) => x === name).length })))

Answer 4

1. Create a Map out of newlst whose keys represent they fruit name and values represent the fruit count.

2. Loop over lst and check if the current fruit is in the Map then increment count otherwise leave as is.

let lst = [{ name: "Apple", total: 4 }, { name: "Mango", total: 9 }, { name: "Orange", total: 6 }, { name: "Passion", total: 2 }];
let newlst = ["Apple", "Orange", "Banana", "Mango", "Apple", "Pineapple", "Passion"];
const m = newlst.reduce((r, f) => r.set(f, (r.get(f) || 0) + 1), new Map());
console.log(
 lst.map((f) => (m.has(f.name) ? { ...f, total: f.total + m.get(f.name) } : f))
)

• Som Shekhar Mukherjee: Does this answer your question? Let me know if you need any help @TM678

Answer 5

You can use Map to create a keyValue pair and update all the existing values in an efficient way.

Const dict = new Map()
lst.forEach(item => dict.set(item.name, item))

When you receive the new array

newlst.forEach(item => {
 if(!dict.has(item)) { // true if you receive a new element not present in lst
 const newObj = {name: item, total: 0}
 dict.set(item, newObj); 
 lts.push(newObj)
 }
 dict.get(item).total++;
})

Since you haven't changed the reference your initial array has now all the values updated. This will be O(n) time complexity.

Answer 6

let lst = [
 { name: 'Apple', total: 4 },
 { name: 'Mango', total: 9 },
 { name: 'Orange', total: 6 },
 { name: 'Passion', total: 2 },
 { name: 'test', total: 1 }
];
let newlst = ["Apple","Orange","Banana","Mango","Apple","Pineapple","Passion"];
lst.map(el=>{
 newlst.indexOf(el.name)>-1 ? el.total=el.total+1 : el
});
console.log(lst)

Answer 7

We can map through the list and filter out items in the newList based on the item being mapped in the list. The length of the filter output will give us the number of occurrences of the item in the newList and based on that we can derive the total logic.

const list = [{name: 'Apple', total: 4}, {name: 'Mango', total: 9}, 
{name: 'Orange', total: 6}, {name: 'Passion', total: 2}];
const newList = ['Apple', 'Orange', 'Banana', 'Mango', 'Apple', 'Pineapple', 'Passion'];
const result = list.map((x) => {
 const numberOfOccurences = newList.filter((y) => y === x.name).length
 return {
 ...x,
 total: x.total + numberOfOccurences
 };
});
console.log(result);