如果存在多个值，则对数组进行过滤以仅返回一个值

Question

I want to filter through an array to return only one city name if more than one of its kind exists.

For example, the ideal output for the bottom code would be:

new york

ohio

mars

---- this is the current output ----

new york

ohio

new york

mars

var people = [{
    name: "jack",
    age: 22,
    city: "new york"
}, {
    name: "john",
    age: 35,
    city: "ohio"
}, {
    name: "travis",
    age: 21,
    city: "new york"
}, {
    name: "david",
    age: 42,
    city: "mars"
}];

for (var i = 0; i < people.length; i++) {
    console.log(people[i].city);   
}

jsfiddle: http://jsfiddle.net/q3nj6ey1/1/

Answer 1

Add to a new array if the city doesn't already exist in it.

var cities  = [];
var numPeople = people.length;
for (var i = 0; i < numPeople; i++) {
    if(cities.indexOf(people[i].city) == -1){
        cities.push(people[i].city);
    }
}

Then you can print your array if you wish:

for(var i=0;i<cities.length;i++){
    console.log(cities[i]);
}