JS: Filter array of objects by max value per category

Question

What is most efficient / elegant way to achieve sql-like filtering effect. I want to filter them and get only that objects which are max value in some group.

This is

Answer 1

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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