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During work, I was given this task : to group elements with similar properties in the array.

In general, the problem is as follows :

var order = [
 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Discharge pressure"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"RCU",
 "equipment":"37 P 552 B",
 "parameter":"Discharge pressure"
 
]

If I group this elements by 'ru', 'area', 'unit', 'tot', 'equipment' and 'parameter', I will get this result :

var result = [
 
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "tot":2,
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "tot":1,
 "equipment":"37 P 552 A",
 "parameter":"Discharge Pressure"
 , 
 "ru":"R401",
 "area":"RFCC",
 "unit":"RCU",
 "tot":1,
 "equipment":"37 P 552 B",
 "parameter":"Discharge Pressure"
 ];

After some experimentation, I came to the following code :

 var groups = _.groupBy(order, function(value) 
 return value.ru + "#" + value.area + "#" + value.unit + "#" + value.equipment + "#" + value.parameter + "#";
 );

 groups = _.map(groups, function(group) 
 return _.extend(group[0], tot: group.length);
 );

Now I have problem how to group the similar result elements. If there is someone around here, please help me. Thanks in advance.

How about this:

var order = [
 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Discharge pressure"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"RCU",
 "equipment":"37 P 552 B",
 "parameter":"Discharge pressure"
 
];
var result = ;
order.forEach(current=>
 let index = -1;
 result.forEach((c,i)=>
 if (c.ru==current.ru && c.area==current.area && c.unit==current.unit && c.tot==current.tot && c.equipment==current.equipment && c.parameter==current.parameter)
 index = i;
 
 );
 // console.log(index);
 if(index==-1)
 result.push(current);
 else
 result[index]["tot"] = result[index]["tot"]+current["tot"];
 
);
console.log(result);

Maybe you can avoid grouping and directly update the tot property of the merged object in your "index" map/object if you encounter similar elements:

Here is a solution that does that with reduce:

const order = [
 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Discharge pressure"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"OFFSITE",
 "equipment":"37 P 552 A",
 "parameter":"Speed"
 , 
 "tot":1,
 "ru":"R401",
 "area":"RFCC",
 "unit":"RCU",
 "equipment":"37 P 552 B",
 "parameter":"Discharge pressure"
 
]

const merged = Object.values(order.reduce((acc, curr) => 
 const key = `$curr.ru#$curr.area#$curr.unit#$curr.equipment#$curr.parameter`;
 if (key in acc) acc[key].tot += 1;
 else acc[key] = Object.assign(, curr);
 return acc;
, ));

console.log(merged);
console.log(merged.map(d => d.ru));