Manipulating data in a different format [duplicate]

Question

I managed to create a query to get some data from the database using the following script:

app.get("/diseases", async (req, res) => {
  const rows = await process.postgresql.query(
    "SELECT ds.disease, ds.symptom FROM diseases ds"
  );
  console.log(rows);
  res.status(200).send(JSON.stringify(rows));
});

The data comes in the following format:

[
  { disease: ' boală hipertensivă', symptom: ' durere toracică' },
  {
    disease: ' boală hipertensivă',
    symptom: ' respirație întretăiată'
  },
  { disease: ' boală hipertensivă', symptom: ' amețeală' },
  { disease: ' boală hipertensivă', symptom: ' astenie' },
  { disease: ' boală hipertensivă', symptom: ' toamnă (Fall)' },
  { disease: ' boală hipertensivă', symptom: ' sincopă' },
  { disease: ' diabet', symptom: ' poliurie' }
]

My question is how to transform this data in a format, like the following:

{"Hypertensive disease": ["Pain chest", "Shortness of breath", "Dizziness", "Asthenia", "Fall", "Syncope", "Vertigo", "Sweat", "Sweating increased", "Palpitation", "Nausea", "Angina pectoris", "Pressure chest"], "Diabetes": ["Polyuria"]}

Answer 1

You're trying to group and transpose the data. The best way is to use .reduce() function on the array. Here's an example:

const arr = [
  { disease: "boal? hipertensiv?", symptom: " durere toracic?" },
  { disease: "boal? hipertensiv?", symptom: " respira?ie întret?iat?" },
  { disease: "boal? hipertensiv?", symptom: " ame?eal?" },
  { disease: "boal? hipertensiv?", symptom: " astenie" },
  { disease: "boal? hipertensiv?", symptom: " toamn? (Fall)" },
  { disease: "boal? hipertensiv?", symptom: " sincop?" },
  { disease: "diabet", symptom: " poliurie" }
];
console.log(arr.reduce((group, row) => {
  // Check if disease group has the disease
  if (typeof group[row.disease] === "undefined") {
    // Initialise an array.
    group[row.disease] = [];
  }
  // Push the symptoms.
  group[row.disease].push(row.symptom.trim());
  // return the updated group.
  return group;
}, {}));

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For the given input above, I get this response:

{
  "boal? hipertensiv?": [
    "durere toracic?",
    "respira?ie întret?iat?",
    "ame?eal?",
    "astenie",
    "toamn? (Fall)",
    "sincop?"
  ],
  "diabet": [
    "poliurie"
  ]
}

Answer 2

return rows.reduce((acc, item) => { if (!!acc[item.disease]) acc[item.disease].push(item.symptom); else acc[item.disease] = [item.symptom]; return acc; }, {})

The reduce function takes two parameters - an iteration processing function, which accumulates a result, and initial result (we put as initial result an empty object {} ).

The iteration processor has two params - the accumulator object acc and current item item, and it should return new (or modified) accumulator object.

On each iteration our function checks if acc already has a field with 'disease' value. If it doesnt' - it creates this field and puts 1 item array [item.symptom] inside. If the field already exists, it pushes a symptom to that array. After we process data we get the object with deseases as keys, and arrays of their symptoms as values.