How to combine two javascript array into one and group by date

问题

Hello I'am new to programming and I stumble upon on grouping array data by date from two arrays.

here is my arrays:

header = [
    {"2019-04-22": "Sun, Apr 22, 2019"},
    {"2019-04-21": "Sat, Apr 21, 2019"},
]

body = [
    {"2019-04-22": "doing customer support”},
    {"2019-04-22": "reply to emails"},
    {"2019-04-21": "send message to customers"},
]

How do I group the arrays into one array as example below

combinearray = {
    "2019-04-22": [
        "Sun, Apr 22, 2019",
        "doing customer support",
        "reply to emails",
    ],
    "2019-04-21": [
        "Sat, Apr 21, 2019",
        "send message to customers",
    ],
}

Grouping two array data by date seems completely not easy for me I'm a beginner to javascript programming. I would appreciate any answers.

回答1:

You can do that in following steps:

First use concat() to combine both arrays i.e header and body
Then use reduce() on that. And pass empty object as second argument(the initial value of accumulator).
In inside reduce() callback use Object.keys()[0] to get date.
Check if the date if date is not already key of accumulator set it to empty [].
Use push() to add the elements to the array.

Note: This will not remove reference to the real object in header and body.

const header = [ {"2019-04-22": "Sun, Apr 22, 2019"}, {"2019-04-21": "Sat, Apr 21, 2019"} ]
const body = [ {"2019-04-22": "doing customer support"}, {"2019-04-22": "reply to emails"}, {"2019-04-21": "send message to customers"}, ]

const res = header.concat(body).reduce((ac,a) => {
  let key = Object.keys(a)[0];
  ac[key] = ac[key] || [];
  ac[key].push(a)
  return ac;
},{})
console.log(res)

However as mentioned in the comments there is no need to have object with keys. Just simple array of the values of that key are enough. For that push() a[key] instead of a.

const header = [ {"2019-04-22": "Sun, Apr 22, 2019"}, {"2019-04-21": "Sat, Apr 21, 2019"} ]
const body = [ {"2019-04-22": "doing customer support"}, {"2019-04-22": "reply to emails"}, {"2019-04-21": "send message to customers"}, ]

const res = header.concat(body).reduce((ac,a) => {
  let key = Object.keys(a)[0];
  ac[key] = ac[key] || [];
  ac[key].push(a[key])
  return ac;
},{})
console.log(res)

回答2:

You can use combine arrays then use reduce

used spread syntax to merge arrays
use reduce to build an object in desired format
Object.entries to get date and it's respective value
Check if the date is already present as key on object or not, if it's already present push the value to it else create a new key

let header = [{"2019-04-22": "Sun, Apr 22, 2019"},{"2019-04-21": "Sat, Apr 21, 2019"},]

let body = [{"2019-04-22": "doing customer support"},{"2019-04-22": "reply to emails"},{"2019-04-21": "send message to customers"},]


let final = [...header,...body].reduce((op,inp) => {
  let [key,value] = Object.entries(inp)[0]
  op[key] = op[key] || []
  op[key].push(value)
  return op
},{})

console.log(final)

来源：https://stackoverflow.com/questions/55877153/how-to-combine-two-javascript-array-into-one-and-group-by-date

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javascript

arrays

object