How would you Filter an array of objects based on a condition

Question

I have an array of objects that looks like this

[
  { id: 1, state: 'PURCHASED' },
  { id: 2, state: 'PURCHASED' },
  { id: 3, state: 'SOLD' },
  { id: 1, state: 'SOLD' },
  { id: 4, state: 'PURCHASED' },
  { id: 6, state: 'SOLD' },
  { id: 9, state: 'PURCHASED' }
]

I would like to filter this array such that I get the items which were PURCHASED but never SOLD . The out would look something like this

[
  { id: 2, state: 'PURCHASED' },
  { id: 3, state: 'SOLD' },
  { id: 4, state: 'PURCHASED' },
  { id: 6, state: 'SOLD' },
  { id: 9, state: 'PURCHASED' }
]

Answer 1

You could find the index by looking for same id and if exist, delete this item.

 var data = [{ id: 1, state: 'PURCHASED' }, { id: 2, state: 'PURCHASED' }, { id: 3, state: 'SOLD' }, { id: 1, state: 'SOLD' }, { id: 4, state: 'PURCHASED' }, { id: 6, state: 'SOLD' }, { id: 9, state: 'PURCHASED' }], result = data.reduce((r, o) => { var index = r.findIndex(q => o.id === q.id); if (index === -1) r.push(o); else r.splice(index, 1); return r; }, []); console.log(result);

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