Creating a unique array from an array of objects

Question

My object demoList:

demoList = [
    {
      id: 1,
      validFrom: "2019-06-01T00:00:00",
      validTo: "2020-06-17T00:00:00",
      xxxM: 50,
      xxxN: 2.2,
      xxxQ45: 2,
      xxxQ100: 1.65,
      xxxQ125: null,
      xxxQ150: null,
      xxxQ250: null,
      xxxQ300: null,
      xxxQ500: null
    },
     {
      id: 2,
      validFrom: "2019-06-01T00:00:00",
      validTo: "2020-06-17T00:00:00",
      xxxM: 51,
      xxxN: 22,
      xxxQ45: 1.4,
      xxxQ100: 1.65,
      xxxQ125: null,
      xxxQ150: 1.7,
      xxxQ250: null,
      xxxQ300: 0.15,
      xxxQ500: null,
      xxxQ700: 15.4
    },
   . . .
];

The array I want to obtain:

["M", "N", "45", "100", "150", "300", "700"]

I want an array of non-empty values starting with xxx and found in the demoList list. How do I do this using angular?

Nick Parsons · Accepted Answer · 2020-01-16 07:58:32Z

1

You can .flatMap() your demoList objects to the Object.entries() of each object. You can keep only those entries which start with "xxx" and the value doesn't equal null by using .filter(). You can then map each key to either the last suffix number on the key or the last character of the key using .match(/\d+|\w$/g). You can then put this mapped array into a new Set() to remove any duplicates. Then you can spread ... this set into an array to convert the set back into an array:

const demoList = [{ id: 1, validFrom: "2019-06-01T00:00:00", validTo: "2020-06-17T00:00:00", xxxM: 50, xxxN: 2.2, xxxQ45: 2, xxxQ100: 1.65, xxxQ125: null, xxxQ150: null, xxxQ250: null, xxxQ300: null, xxxQ500: null }, { id: 2, validFrom: "2019-06-01T00:00:00", validTo: "2020-06-17T00:00:00", xxxM: 51, xxxN: 22, xxxQ45: 1.4, xxxQ100: 1.65, xxxQ125: null, xxxQ150: 1.7, xxxQ250: null, xxxQ300: 0.15, xxxQ500: null, xxxQ700: 15.4 } ];

const res = [...new Set(
  demoList.flatMap(Object.entries)
          .filter(([k, v]) => k.startsWith("xxx") && v !== null)
          .map(([k]) => k.match(/\d+|\w$/g).pop())
)];

console.log(res);

answered Jan 16, 2020 at 7:58

Nick Parsons

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3 Comments

devedev Over a year ago

trying with stackblitz "ERROR Error: (intermediate value).slice is not a function" error

Nick Parsons Over a year ago

@devedev I am not using .slice() in my code, sounds like an unrelated issue

devedev Over a year ago

How can I optimize this code ` let barems: String[] = []; this.demoList.forEach(list=> { let keys: string[] = Object.getOwnPropertyNames(list); keys.forEach(key => { if(key.includes("xxx") && list[key] != null){ if(barems.indexOf(key) == -1){ barems.push(key); console.log(key); } } }) }) `

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