I have my example array:
var person = [{
firstName:"John",
lastName:"Doe",
age:46
},
{
firstName:"Alexander",
lastName:"Bru",
age:46
},
{
firstName:"Alex",
lastName:"Bruce",
age:26
}];
Simple person.length gives me the length of my array, but I need to merge values when the age is the same. So if two people have same age return 1 no 2. Sorry for my bad English, I can made a mistakes.
Use Array#forEach method with an object reference for age.
var person = [{
firstName: "John",
lastName: "Doe",
age: 46
}, {
firstName: "Alexander",
lastName: "Bru",
age: 46
}, {
firstName: "Alex",
lastName: "Bruce",
age: 26
}];
// object for storing reference to age
var obj = {},
res = 0;
// iterate and count
person.forEach(function(v) {
// check age already not defined
if (!obj[v.age]) {
// define the property
obj[v.age] = true;
// increment count
res++;
}
});
console.log(res);
Filter the array down to only those elements for which a find on the array for the first element with the same age yields the element itself, then take the length of the result:
array.filter(o1 => o1 === array.find(o2 => o2.age === o1.age)).length
Another idea involves using a little function called uniqueCount, which counts the number of unique values in a (sorted) array:
function uniqueCount(a) {
return a.reduce((cnt, elt, i) => a[i] === a[i-1] ? cnt : cnt + 1), 0);
}
Now you can create an array of all the ages, and do a count of its unique elements on it:
uniqueCount(array.map(e => e.age).sort(numeric))
If you are allowed to, you could add all the ages to a set and take its size.
const people = [{
firstName: "John",
lastName: "Doe",
age: 46
}, {
firstName: "Alexander",
lastName: "Bru",
age: 46
}, {
firstName: "Alex",
lastName: "Bruce",
age: 26
}];
const ages = new Set(people.map(person => person.age));
console.log(ages.size)
