从对象数组创建一个新对象，并按特定的匹配键/值分组

Question

Example of the object data I am dealing with

var myData = [{
  "name": "John",
  "age": 30,
  "interest": "Baseball"
},
{
  "name": "Bob",
  "age": 21,
  "interest": "Baseball"
},
{
  "name" : "Sally",
  "age" : 29,
  "interest": "Tennis"
}]

I am trying to figure out the easiest way to group them by interests. I am open to using lodash or underscore, but I cannot get the final result to look like this....

I want this to be the output:

[{ "Baseball" : [{
                  "name": "John",
                  "age" : 30
                 },
                 {
                  "name" : "Bob",
                  "age" : 21
                 }]
 },
 { "Tennis" : [{
                 "name" : "Sally",
                 "age" : 21
               }]
 }];

Basically, each interest becomes a new object key containing all of the matched values within arrays.

I am having trouble constructing this output. Any assistance would be greatly appreciated. I prefer to use lodash/underscore to keep things very easy.

Thank you!

Answer 1

A group-by operation can be done by matching values in a dictionary (hashtable). In JavaScript all objects are dictionaries with property-names as the keys, for values we use arrays.

For example (press the "Run code snippet" button below to see the results):

 function groupBy( input, propertyName ) { var output = {}; for(var i = 0; i < input.length; i++) { var groupByValue = input[i][propertyName]; if( !(groupByValue in output) ) { output[ groupByValue ] = []; } var dolly = cloneObjectButIgnoreProperty( input[i], propertyName ); output[ groupByValue ].push( dolly ); } return output; } function cloneObjectButIgnoreProperty( value, ignorePropertyName ) { var dolly = {}; var propertyNames = Object.keys( value ); for( var i = 0; i < propertyNames .length; i++ ) { var propertyName = propertyNames[i]; if( propertyName == ignorePropertyName ) continue; dolly[propertyName ] = value[propertyName ]; } return dolly; } var myData = [ { "name": "John", "age": 30, "interest": "Baseball" }, { "name": "Bob", "age": 21, "interest": "Baseball" }, { "name" : "Sally", "age" : 29, "interest": "Tennis" } ]; var groupedByInterest = groupBy( myData, 'interest' ); console.log( "By interest:" ); console.log( groupedByInterest ); var groupedByName = groupBy( myData, 'name' ); console.log( "By name:" ); console.log( groupedByName ); var groupedByAge = groupBy( myData, 'age' ); console.log( "By age:" ); console.log( groupedByAge ); 

Answer 2

You could use Array.reduce for this:

 var myData = [ { "name": "John", "age": 30, "interest": "Baseball" }, { "name": "Bob", "age": 21, "interest": "Baseball" }, { "name" : "Sally", "age" : 29, "interest": "Tennis" }]; var result = myData.reduce(function(entities, obj) { entities[obj.interest] = (entities[obj.interest] || []).concat({ name: obj.name, age: obj.age }); return entities; }, {}); console.log(result); 

A little bit more general approach:

 function groupBy(data, key, tFunc) { mapFunc = (typeof tFunc === "function")? tFunc: function(o) { return o }; return (Array.isArray(data)?data:[]).reduce(function(entities, o) { if(o[key]) { entities[o[key]] = (entities[o[key]] || []).concat(tFunc(o)); } return entities; }, {}); } // test code var myData = [ { "name": "John", "age": 30, "interest": "Baseball" }, { "name": "Bob", "age": 21, "interest": "Baseball" }, { "name" : "Sally", "age" : 29, "interest": "Tennis" }]; var result = groupBy(myData, "interest", function(o) { return { name: o.name, age: o.age}}); console.log(result); var result2 = groupBy(myData, "age", function(o) { return o.name}); console.log(result2); 

Answer 3

The solution using Array.prototype.reduce() function:

 var myData = [{ "name": "John", "age": 30, "interest": "Baseball" }, { "name": "Bob", "age": 21, "interest": "Baseball" }, { "name" : "Sally", "age" : 29, "interest": "Tennis" }], result = myData.reduce(function (r, o) { r[o.interest] = r[o.interest] || []; r[o.interest].push({name: o.name, age: o.age}); return r; }, {}); console.log(result); 

Answer 4

 var myData = [{name:"John",age:30,interest:"Baseball"},{name:"Bob",age:21,interest:"Baseball"},{name:"Sally",age:29,interest:"Tennis"}], result = [], interests = [...new Set(myData.map(v => v.interest))]; interests.forEach(v => result.push({ [v] : [] })); myData.forEach((v,i) => result.forEach((c,i) => Object.keys(c)[0] == v.interest ? result[i][v.interest].push({name: v.name, age: v.age}) : c)) console.log(result);