how can I use map before reduce in an object of an array-CodePudding

I want to sum each price with pervious value as a new array this is my object and my final array I except with my reducer I write

data=[{price: 2, volume: 123}
{price: 3, volume: 123}
{price: 4, volume: 254}
{price: 1, volume: 444}
{price: 5, volume: 555}]

finaldata=[{price: 2, volume: 555}
1: {price: 5, volume: 777}
2: {price: 9, volume: 5000}
3: {price: 10, volume: 8000}
4: {price: 15, volume: 4000}]

 const test = buy.map((items, index) =>
      items.reduce((prev, curr, currIndex) => {
        return index >= currIndex ? { volume: (prev?.volume || 0)   curr?.volume } : 0;
      }, 0)
    );
    cons

CodePudding user response：

It's better to use reduce for sum each price with pervious value as a new array, not map

const data=[{price: 2, volume: 123},
    {price: 3, volume: 123},
    {price: 4, volume: 254},
    {price: 1, volume: 444},
    {price: 5, volume: 555}]
    
    
const result = 
  data.reduce((acc, curr, currIndex) => {
  const lastItem = acc[acc.length - 1];
  acc.push({ ...curr, price: lastItem ? lastItem.price   curr.price : curr.price })
  return acc;
}, [])
console.log(result)

CodePudding user response：

i would use like this, first i concat all data from first data with finaldata then i group it, if price is same then it will increase the volume

const  data = [
    {price: 2, volume: 123},
    {price: 3, volume: 123},
    {price: 4, volume: 254},
    {price: 1, volume: 444},
    {price: 5, volume: 555}
]

const finaldata = [
    {price: 2, volume: 555},
    {price: 5, volume: 777},
    {price: 9, volume: 5000},
    {price: 10, volume: 8000},
    {price: 15, volume: 4000}
]

const result = [...data].concat(finaldata).reduce((previous, {price, volume}) => {
    const find = previous.find(item => item.price === price);
    if (find) {
        find.volume = find.volume   volume
    } else {
        previous.push({price, volume})
    }
    return previous
}, [])

console.log(result)

CodePudding user response：

You can also achieve this with a single line of code by using Array.map() method.

Live Demo :

const data=[{price: 2, volume: 123},
            {price: 3, volume: 123},
            {price: 4, volume: 254},
            {price: 1, volume: 444},
            {price: 5, volume: 555}];
            
const finalData = data.map((obj, index) => {
  if (index < data.length - 1) data[index   1].price = data[index   1].price   obj.price;
  return obj;
});

console.log(finalData);

CodePudding user response：

I publish my solution here because I think it is easier to understand than the other solutions.

const data = [
  { price: 2, volume: 123 },
  { price: 3, volume: 123 },
  { price: 4, volume: 254 },
  { price: 1, volume: 444 },
  { price: 5, volume: 555 }
]

let priceAccum = 0
const res = data.map((item) => {
  priceAccum  = item.price
  return { ...item, price: priceAccum }
})

console.table(res)

We accumulate price in a variable and replace the item's price with the accumulated value. The code is not a pure function. Using reduce purifies it, but it sacrifices simplicity.

CodePudding user response：

There are so many solutions for all tastes in this post. My approach is a .reduce with a complex accamulator in a non-mutable way:

const inputData = [{price:2,volume:123},{price:3,volume:123},{price:4,volume:254},{price:1,volume:444},{price:5,volume:555}];

const runningTotals = inputData
  .reduce((acc, item) => ({
    total: acc.total   item.price,
    data: [...acc.data, { ...item, price: acc.total   item.price }],
  }), { total:0, data:[] })
  .data;
  
console.log(runningTotals);

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