I have an array of data get from the server(ordered by date):
[ {date:"2012-8", name:"Tokyo"}, {date:"2012-3", name:"Beijing"}, {date:"2011-10", name:"New York"} ]
I'd like to :
2012, I need Tokyo namenamewhich data structure should I use to make this effective ?
because the array could be large, I prefer not to loop the array to find something
Since it appears that the data is probably already sorted by descending date you could use a binary search on that data to avoid performing a full linear scan.
To handle the unstated requirement that changing the date will then change the ordering, you would need to perform two searches, which as above could be binary searches. Having found the current index, and the index where it's supposed to be, you can use two calls to Array.splice() to move the element from one place in the array to another.
To handle searches by name, and assuming that each name is unique, you should create a secondary structure that maps from names to elements:
var map = {};
for (var i = 0, n = array.length; i < n; ++i) {
var name = array[i].name;
map[name] = array[i];
}
You can then use the map array to directly address requirements 2 and 3.
Because the map elements are actually just references to the array elements, changes to those elements will happen in both.
loop through the array until you find the first matching element?Assuming you are using unique cities, I would use the city names as a map key:
cities = {
Tokyo: {
date: "2012-8"
},
New York: {
date: "2011-10"
}
}
To search by date:
function byDate(date) {
for(el in cities) {
if(cities.hasOwnProperty(el) && cities[el].date === date)
return el;
}
}
get the name of the first element whose date is in a given year how to do this?
cities object is unordered, whereas the OP's original data is an array, with an implicit ordering.
Just for the record: without redesigning your date structure you could use sorting combined with the Array filter or map method:
function sortByDate(a,b){
return Number(a.date.replace(/[^\d]+/g,'')) >
Number(b.date.replace(/[^\d]+/g,''));
}
var example = [ {date:"2012-8", name:"Tokyo"},
{date:"2012-3", name:"Beijing"},
{date:"2011-10", name:"New York"} ]
.sort(sortByDate);
//first city with year 2012 (and the lowest month of that year)
var b = example.filter(function(a){return +(a.date.substr(0,4)) === 2012})[0];
b.name; //=> Beijing
//year of a given city
var city = 'Tokyo';
var c = example.filter(function(a){return a.city === city;})[0];
c.year; //=> 2012
//change year of 'New York', and resort data
var city = 'New York', date = '2010-10';
example = example.map(
function(a){if (a.name === city) {a.date = date;} return a;}
).sort(sortByDate);
