CODEWITHSUNDEEP
javascriptoptimizationsortingcomparison
ariel
ariel

Reputation: 16140

Optimizing this double comparison result for sorting in javascript

Usually while sorting you do:

if (x < y) return -1
else if (x > y) return 1
else return 0

or

return ((x > y) ? 1 : ((x < y)) ? -1 : 0))

Two comparisons for what seems can be accomplished with only one. In assembly all you have to do is subtract both to a register, check if is negative, check if is zero. The problem is in javascript if we were to subtract:

var sub = (x - y);
return (sub == 0 ? 0 : ((sub < 0) ? -1 : 1))

This would end up with even more code to be executed.

So, some questions:

Upvotes: 1

Views: 502

Answers (3)

kennebec
kennebec

Reputation: 104810

sorting alphabetically can be done with array.sort(), but if you want a case insensitive sort you do need to test if the strings are the same, or if one is greater or less than the other. 

array.sort(function(a,b){
  a=a.toLowerCase();
  b=b.toLowerCase();
  if(a==b) return 0;
  return a>b? 1:-1;
}

Worrying about an extra comparison is beside the point here, the conversion toLowerCase is what eats up cycles. SO don't use toLowerCase unless you need it.

Numbers, as has been shown, are simple-

array.sort(function(a,b){ return a-b});

Upvotes: 1

smartbloke
smartbloke

Reputation: 121

Usually the sort algorithm is not looking specifically for -1 or +1, just <0 or >0. The comparison function in this case could be as simple as

return x - y ;

Upvotes: 1

lonesomeday
lonesomeday

Reputation: 237975

In Javascript, sort does not have to return -1, 0 or 1. It can return any number. This means that you only need to subtract one number from the other to compare them.

The MDC docs for Array.sort suggest this implementation:

function compareNumbers(a, b)
{
  return a - b;
}

var nums = [34, 56, 1, 42, 63];
nums.sort(compareNumbers);
// [1, 34, 42, 56, 63]

Upvotes: 2

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