How do I sort an array of objects based on the ordering of another array?

Question

I have a list of objects:

[ { id: 4, name:\'alex\' }, { id: 3, name:\'jess\' }, { id: 9, name:\'...\' }, { id: 1, name:\'abc\' } ]

I have a

Answer 1

Well, the simple answer would be, "for a set of data this small, anything less costly than an infinite loop will be basically unnoticeable." But let's try to answer this "right."

There's no rhyme or reason to the order in the second array, it's just a list of foreign keys (to use SQL terminology) on the primary keys of the first array. So, thinking of them as keys, and that we want efficient lookup of those keys, a hash table (object) would probably "sort" this the quickest, in an O(n) fashion (2*n, really) assuming the first array is called objArray and the second array is called keyArray:

// Create a temporary hash table to store the objects
var tempObj = {};
// Key each object by their respective id values
for(var i = 0; i < objArray.length; i++) {
    tempObj[objArray[i].id] = objArray[i];
}
// Rebuild the objArray based on the order listed in the keyArray
for(var i = 0; i < keyArray.length; i++) {
    objArray[i] = tempObj[keyArray[i]];
}
// Remove the temporary object (can't ``delete``)
tempObj = undefined;

And that should do it. I can't think of any method that doesn't require two passes. (Either one after the other, like this, or by passing multiple times through the array and spliceing out the found elements, which can get costly with backwards-sorted data, for instance.)