Finding the max value of an attribute in an array of objects

问题:

I'm looking for a really quick, clean and efficient way to get the max "y" value in the following JSON slice:

[{"x":"8/11/2009","y":0.026572007},{"x":"8/12/2009","y":0.025057454},{"x":"8/13/2009","y":0.024530916},{"x":"8/14/2009","y":0.031004457}] 

Is a for-loop the only way to go about it? I'm keen on somehow using Math.max.

回答1:

Math.max.apply(Math,array.map(function(o){return o.y;})) 

回答2:

One way would be to use Array reduce..

const max = data.reduce(function(prev, current) {     return (prev.y > current.y) ? prev : current }) //returns object 

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce http://caniuse.com/#search=reduce (IE9 and above)

If you don't need to support IE (only Edge), or can use a pre-compiler such as Babel you could use the more terse syntax.

const max = data.reduce((prev, current) => (prev.y > current.y) ? prev : current) 

回答3:

clean and simple ES6 (Babel)

const maxValueOfY = Math.max(...arrayToSearchIn.map(o => o.y)); 

回答4:

Well, first you should parse the JSON string, so that you can easily access it's members:

var arr = $.parseJSON(str); 

Use the map method to extract the values:

arr = $.map(arr, function(o){ return o.y; }); 

Then you can use the array in the max method:

var highest = Math.max.apply(this,arr); 

Or as a one-liner:

var highest = Math.max.apply(this,$.map($.parseJSON(str), function(o){ return o.y; })); 

回答5:

I'd like to explain the terse accepted answer step-by-step:

var objects = [{ x: 3 }, { x: 1 }, { x: 2 }];  // array.map lets you extract an array of attribute values var xValues = objects.map(function(o) { return o.x; }); // es6 xValues = Array.from(objects, o => o.x);  // function.apply lets you expand an array argument as individual arguments // So the following is equivalent to Math.max(3, 1, 2) // The first argument is "this" but since Math.max doesn't need it, null is fine var xMax = Math.max.apply(null, xValues); // es6 xMax = Math.max(...xValues);  // Finally, to find the object that has the maximum x value (note that result is array): var maxXObjects = objects.filter(function(o) { return o.x === xMax; });  // Altogether xMax = Math.max.apply(null, objects.map(function(o) { return o.x; })); var maxXObject = objects.filter(function(o) { return o.x === xMax; })[0]; // es6 xMax = Math.max(...Array.from(objects, o => o.x)); maxXObject = objects.find(o => o.x === xMax);   document.write('
objects: ' + JSON.stringify(objects) + '
'); document.write('
xValues: ' + JSON.stringify(xValues) + '
'); document.write('
xMax: ' + JSON.stringify(xMax) + '
'); document.write('
maxXObjects: ' + JSON.stringify(maxXObjects) + '
'); document.write('
maxXObject: ' + JSON.stringify(maxXObject) + '
');

Further information:

• Math.max.apply()
• Array.prototype.map()
• Array.from()
• Function.prototype.apply()
• Array.prototype.filter()
• Array.prototype.find()

回答6:

if you (or, someone here) are free to use lodash utility library, it has a maxBy function which would be very handy in your case.

hence you can use as such:

_.maxBy(jsonSlice, 'y'); 

回答7:

var max = 0;                 jQuery.map(arr, function (obj) {   if (obj.attr > max)     max = obj.attr; }); 

回答8:

use this both :    obj = Math.max.apply(Math,data.map(function(o){return o.partsCount;}));  Array.prototype.max = function() {   return Math.max.apply(null, this); }; 

回答9:

Based on great answer from @tobyodavies.

Try this out below working example.

var t = [{"x":"8/11/2009","y":0.026572007},{"x":"8/12/2009","y":0.025057454},{"x":"8/13/2009","y":0.024530916},{"x":"8/14/2009","y":0.031004457}] Math.max.apply(Math,t.map(function(o){return o.y;})) 

回答10:

function getMaxProperty(arrayOfObjects, property) {     const arrayOfValues = arrayOfObjects.map(obj => obj[property]);     return Math.max(...arrayOfValues); } 

回答11:

A simple reduce with negative infinity as default? Does what you need in a single iteration/operation...

array.reduce((last,current)=>current.y>last?current.y:last,-Infinity) 

回答12:

Or a simple sort! Keeping it real :)

array.sort((a,b)=>a.y

回答13:

ES6 solution

Math.max(...array.map(function(o){return o.y;}))

For more details see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/max

文章来源: Finding the max value of an attribute in an array of objects