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Find the number of times a value of an object property occurs in an array with JavaScript?
For this, use the concept of reduce(). Following is the code −
Example
const subjectDetails =
[
{
subjectId: '101',
subjectName: 'JavaScript'
},
{
subjectId: '102',
subjectName: 'Java'
},
{
subjectId: '103',
subjectName: 'JavaScript'
}
];
console.log([...subjectDetails.reduce((obj1, obj2) => {
if (obj1.has(obj2.subjectName)){
obj1.get(obj2.subjectName).frequency++;
} else {
obj1.set(obj2.subjectName, { subjectName: obj2.subjectName,
frequency: 1 });
}
return obj1;
}, new Map()).values()]);To run the above program, you need to use the following command −
node fileName.js.
Here, my file name is demo144.js.
Output
This will produce the following output −
PS C:\Users\Amit\JavaScript-code> node demo144.js
[
{ subjectName: 'JavaScript', frequency: 2 },
{ subjectName: 'Java', frequency: 1 }
]
Updated on: 11-Sep-2020
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