array of objects manipulation in js

Question

I have an array of object as below.

data: [ {col: ['amb', 1, 2],} , {col: ['bfg', 3, 4], },]

From above, I need to get array of array as below.

[ [{a: 'amb',b: [1], c: 'red'}, {a: 'amb',b: [2], c: 'orange'}], 
  [{a: 'bfg',b: [3], c: 'red'}, {a: 'bfg',b: [4], c: 'orange'}] 
]

My attempt is as below.

let arrInner: Array<any> = []
let arrOuter: Array<Array<any>> = []

_.forEach(data, (item, i) => {
    //create two objects redObj and orangeObj

    redObj = {
      a: item.col[0].toString(),
      b: [item.col[1] as number],
      c: 'red'
    }
    orangeObj = {
      a: item.col[0].toString(),
      b: [item.col[2] as number],
      c: 'orange'
    }
    
    //put those two objects to array
    arrInner.push(redObj)
    arrInner.push(orangeObj)
    
    //assign that array to another array
    arrOuter[i] = arrInner
})

But when I print the arrOuter, it is not my expected output. Where I was wrong and how can I fix this?

"Where I was wrong and how can I fix this?" I suggest that you add console.log() to see what is happening in your code to figure out what is wrong. You might want to rethink your entire approach, though. If I were solving this, I would break it into smaller pieces. For example, I would start with ['amb', 1, 2] and convert it into [{a: 'amb',b: [1]}, {a: 'amb',b: [2]}]. Don't try to eat the entire elephant at once. — Code-Apprentice
– Code-Apprentice, Commented Jul 1, 2021 at 19:42
You also might want to look into the map() function instead of forEach(). — Code-Apprentice
– Code-Apprentice, Commented Jul 1, 2021 at 19:43

Barmar · Accepted Answer · 2021-07-01 19:44:11Z

1

You need to create a new arrInner each time through the forEach loop. Then push that onto arrOuter.

let arrOuter: Array <Array <any>> = []

_.forEach(data, (item, i) => {

  //create two objects redObj and orangeObj

  redObj = {
    a: item.col[0].toString(),
    b: [item.col[1] as number],
    c: 'red'
  }
  orangeObj = {
    a: item.col[0].toString(),
    b: [item.col[2] as number],
    c: 'orange'
  }

  //put those two objects to array
  let arrInner = [redObj, orangeObj]

  //assign that array to another array
  arrOuter.push(arrInner)
})

answered Jul 1, 2021 at 19:44

Barmar

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