How do you apply a custom sort to an array?

Question

I'd like to sort an array in a customized way.

Example would be a student's classlevel:

_.sortBy(["Junior","Senior","Freshman","Sophomore"], function(classlevel){  
    // ??  
})

Ideally, the sort should return:

["Freshman","Sophomore","Junior","Senior"]

I'm thinking if I could pre-rank the classlevels ahead of time like this:

var classlevelRanked = [{ class: "Junior",
   rank: 3
 },{ class: "Senior",
   rank: 4
 },{ class: "Freshman",
   rank: 1
 },{ class: "Sophomore",
   rank: 2
 }]

and then apply a sort via:

_.sortBy(classlevelRanked, function(classlevel){  
  return classlevel.rank;  
})

But then I have to strip out the ranks by doing:

.map(function(classlevel){  
    return classlevel["class"];  
})

Is there a more direct way to do this without pre-ranking the classlevels and then stripping it out afterwards?

Thank you.

Answer 1

You should be able to do something like this:

_.sortBy(["Junior","Senior","Freshman","Sophomore"], function(element){  
    var rank = {
        "Junior" : 3,
        "Senior" : 4,
        "Freshman" :1,
        "Sophomore" :2
    };

    return rank[element];
});

Fiddle:

http://jsfiddle.net/hKQj8/

---

Alternatively, if rank is a constant that may be useful elsewhere, you can define it outside of the _.sortBy expression and use _.propertyOf for a more declarative style:

var rank = {
    "Junior" : 3,
    "Senior" : 4,
    "Freshman" :1,
    "Sophomore" :2
};

_.sortBy(["Junior","Senior","Freshman","Sophomore"], _.propertyOf(rank));

Answer 2

In addition to Jason's answer:

var list = _.sortBy([{name:"Junior"},{name:"Senior"},{name:"Freshman"},{name:"Sophomore"}], function(element){  
    var rank = {
        "Junior" : 3,
        "Senior" : 4,
        "Freshman" :1,
        "Sophomore" :2
    };

    return rank[element.name];
});

 console.dir(list);

It will help to sort array of objects