JavaScript code to fetch range of dates from array of objects depending on one attribute of the array using array.reduce()

Question

var developers = [
{ name: "Joe", age: 23, overallLevel: "high", date: "Aug 14, 2015" },
{ name: "Sue", age: 28, overallLevel: "advanced", date: "Aug 11, 2015" },
{ name: "Jon", age: 32, overallLevel: "high", date: "Aug 10, 2015" },
{ name: "Bob", age: 24, overallLevel: "high", date: "Sept 07, 2015" },
{ name: "Johnson", age: 23, overallLevel: "advanced", date: "Aug 20, 2015" },
{ name: "Paul", age: 25, overallLevel: "basic", date: "Jan 30, 2016" },
{ name: "Jane", age: 27, overallLevel: "intermediate", date: "Aug 30, 2016" },
{ name: "Chris", age: 20, overallLevel: "basic", date: "Aug 1, 2016" },
{ name: "Susan", age: 25, overallLevel: "basic", date: "Dec 12, 2015" },
{ name: "Jenny", age: 23, overallLevel: "intermediate", date: "Aug 30, 2016" },
{ name: "Stone", age: 25, overallLevel: "basic", date: "June 13, 2016" },
]

Following is the data extracted from array which indicates levels followed by their dates.

"high" : Aug 10, 2015, Aug 14, 2015, Sept 07, 2015

"advanced" : Aug 11, 2015, Aug 20, 2015

"basic" : Jan 30, 2016, Aug 1, 2016, Dec 12, 2015, June 13, 2016,

"intermediate" : Aug 30, 2016, Aug 30, 2016

Expected output: Require the range of min and max date i.e shown further

{ high : Aug 10, 2015 - Sept 07,2015, advanced : Aug 11, 2015 - Aug 20,2015, basic : Dec 12, 2015 - Aug 1,2016, intermediate : Jan 30,2016 }

This is what i was able to get the count of overallLevel for grouping purpose.

var developers = [
{ name: "Joe", age: 23, overallLevel: "high", date: "Aug 14, 2015" },
{ name: "Sue", age: 28, overallLevel: "advanced", date: "Aug 11, 2015" },
{ name: "Jon", age: 32, overallLevel: "high", date: "Aug 10, 2015" },
{ name: "Bob", age: 24, overallLevel: "high", date: "Sept 07, 2015" },
{ name: "Johnson", age: 23, overallLevel: "advanced", date: "Aug 20, 2015" },
{ name: "Paul", age: 25, overallLevel: "basic", date: "Jan 30, 2016" },
{ name: "Jane", age: 27, overallLevel: "intermediate", date: "Aug 30, 2016" },
{ name: "Chris", age: 20, overallLevel: "basic", date: "Aug 1, 2016" },
{ name: "Susan", age: 25, overallLevel: "basic", date: "Dec 12, 2015" },
{ name: "Jenny", age: 23, overallLevel: "intermediate", date: "Aug 30, 2016" },
{ name: "Stone", age: 25, overallLevel: "basic", date: "June 13, 2016" },
],
    overallLevel = developers.reduce(function (r, a) {
        r[a.overallLevel] = (r[a.overallLevel] || 0) + 1;
        return r;
    }, {});

console.log(overallLevel);

Please visit this : https://jsfiddle.net/Saily/6nzxd6ss/

Where is your script ? You are suppose to share your efforts as well.. — Rayon
– Rayon, Commented Jun 1, 2016 at 11:54
@SailyJadhav, This is just what Nina had answered ain't it ? — Rayon
– Rayon, Commented Jun 1, 2016 at 12:03
LOC's get reduced this is the reason to use reduce @NinaScholz — Saily Jadhav
– Saily Jadhav, Commented Jun 1, 2016 at 12:10
You have to actually put in some of your own effort. This isn't a "write code for me" site. Also, you still haven't clearly conveyed why you need to use .reduce() for this. — JLRishe
– JLRishe, Commented Jun 1, 2016 at 12:29

Redu · Accepted Answer · 2016-06-01 20:06:01Z

I also enjoy using reduces. It's very handy for a lot of cases.

var developers = [
{ name: "Joe", age: 23, overallLevel: "high", date: "Aug 14, 2015" },
{ name: "Sue", age: 28, overallLevel: "advanced", date: "Aug 11, 2015" },
{ name: "Jon", age: 32, overallLevel: "high", date: "Aug 10, 2015" },
{ name: "Bob", age: 24, overallLevel: "high", date: "Sept 07, 2015" },
{ name: "Johnson", age: 23, overallLevel: "advanced", date: "Aug 20, 2015" },
{ name: "Paul", age: 25, overallLevel: "basic", date: "Jan 30, 2016" },
{ name: "Jane", age: 27, overallLevel: "intermediate", date: "Aug 30, 2016" },
{ name: "Chris", age: 20, overallLevel: "basic", date: "Aug 1, 2016" },
{ name: "Susan", age: 25, overallLevel: "basic", date: "Dec 12, 2015" },
{ name: "Jenny", age: 23, overallLevel: "intermediate", date: "Aug 30, 2016" },
{ name: "Stone", age: 25, overallLevel: "basic", date: "June 13, 2016" },
],
reduced = developers.reduce((p,c) => {var d = new Date(c.date);
                                      p[c.overallLevel] ? d < p[c.overallLevel][0] && d < p[c.overallLevel][1] ? p[c.overallLevel][0] = d
       	                                                                                                       : p[c.overallLevel][1] = d
                                                        : p[c.overallLevel] = [d,d];
                                      return p},{});
reduced = Object.keys(reduced).reduce((p,c) => (p[c] = p[c].map(e => e.toDateString(2)), p),reduced);
       
console.log(reduced);

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