JS: Filter array of objects by max value per category

Solution 1:

Reduce the array to an object, using the name property as the key. For each item, check if the item that exists in the accumulator has a higher value than the current item, and if not replace it with the current item. Convert back to an array with Object.values():

const arr = [{"name":"bathroom","value":54,"timeStamp":1562318089713},{"name":"bathroom","value":55,"timeStamp":1562318090807},{"name":"bedroom","value":48,"timeStamp":1562318092084},{"name":"bedroom","value":49,"timeStamp":1562318092223},{"name":"room","value":41,"timeStamp":1562318093467}]

const result = Object.values(arr.reduce((r, o) => {
  r[o.name] = (r[o.name] && r[o.name].value > o.value) ? r[o.name] : o

  return r
}, {}))

console.log(result)

Solution 2:

I love to use lodash for stuff like this. It's very functional and therefore very clear and straightforward.

Take a look at the following code:

const DATA = [
  {
    name: "bathroom",
    value: 54,
    timeStamp: 1562318089713
  },
  {
    name: "bathroom",
    value: 55,
    timeStamp: 1562318090807
  },
  {
    name: "bedroom",
    value: 48,
    timeStamp: 1562318092084
  },
  {
    name: "bedroom",
    value: 49,
    timeStamp: 1562318092223
  },
  {
    name: "room",
    value: 41,
    timeStamp: 1562318093467
  }
];

let max = _
  .chain(DATA)
  .groupBy('name')
  .sortBy('value')
  .map(o => _(o).reverse().first())
  .flatten()
  .value();

console.log(max); // returns [{"name":"bathroom","value":55,"timeStamp":1562318090807},{"name":"bedroom","value":49,"timeStamp":1562318092223},{"name":"room","value":41,"timeStamp":1562318093467}]

Solution 3:

Here is another reduce alternative :

var arr = [{"name":"bathroom","value":54,"timeStamp":1562318089713},{"name":"bathroom","value":55,"timeStamp":1562318090807},{"name":"bedroom","value":48,"timeStamp":1562318092084},{"name":"bedroom","value":49,"timeStamp":1562318092223},{"name":"room","value":41,"timeStamp":1562318093467}];

var obj = arr.reduce((r, o) => (o.value < (r[o.name] || {}).value || (r[o.name] = o), r), {});

console.log( Object.values(obj) );

Solution 4:

What is most efficient / elegant way to achieve sql-like filtering effect.

You could take functions for every step and pipe all functions for a single result.

For example in SQL, you would have the following query:

SELECT name, value, MAX(timeStamp) 
FROM data 
GROUP BY name;

With an SQL like approach, you could group first and take the max object out of the result sets.

result = pipe(
    groupBy('name'),
    select(max('timeStamp'))
)(data);

const
    pipe = (...functions) => input => functions.reduce((acc, fn) => fn(acc), input),
    groupBy = key => array => array.reduce((r, o) => {
        var temp = r.find(([p]) => o[key] === p[key])
        if (temp) temp.push(o);
        else r.push([o]);
        return r;
    }, []),
    max = key => array => array.reduce((a, b) => a[key] > b[key] ? a : b),
    select = fn => array => array.map(fn);


var data = [{ name: 'bathroom', value: 54, timeStamp: 1562318089713 }, { name: 'bathroom', value: 55, timeStamp: 1562318090807 }, { name: 'bedroom', value: 48, timeStamp: 1562318092084 }, { name: 'bedroom', value: 49, timeStamp: 1562318092223 }, { name: 'room', value: 41, timeStamp: 1562318093467 }],
    result = pipe(
        groupBy('name'),
        select(max('timeStamp'))
    )(data);

console.log(result);

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JS: Filter array of objects by max value per category

Solution 1:

Solution 2:

Solution 3:

Solution 4:

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