javascript - Min and max in multidimensional array

Question

My array is:

var a = new Array();
a[0] = {x: 10,y: 10};
a[1] = {x: 20,y: 50};
a[2] = {x: 30,y: 20};
a[3] = {x: 10,y: 10};

var min = Math.min.apply(null, a.x) doesn't work. Some ideas?

Answer 1

You had the right idea with .apply but you need to pass a collection of the x values.

var xVals = a.map(function(obj) { return obj.x; });
var min = Math.min.apply(null, xVals);

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The .map() method makes a new Array comprised of whatever you returned in each iteration.

[10, 20, 30, 10]

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Then passing the Array as the second argument to .apply will distribute the members of the Array as individual arguments. So it's as though you did this:

Math.min(10, 20, 30, 10) // 10

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But since you need to .map(), you might as well skip the Math.min, and just use .reduce instead.

var min = a.reduce(function(min, obj) { 
                      return obj.x < min ? obj.x : min; 
                   }, Infinity);