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

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

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.

Solutions/Answers:

Solution 1:

To find the maximum y value of the objects in array:

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

Solution 2:

Find the object whose property “X” has the greatest value in an array of objects

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)

Solution 3:

clean and simple ES6 (Babel)

const maxValueOfY = Math.max(...arrayToSearchIn.map(o => o.y), 0);

The second parameter should ensure a default value if arrayToSearchIn is empty.

Solution 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; }));

Solution 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('<p>objects: ' + JSON.stringify(objects) + '</p>');
document.write('<p>xValues: ' + JSON.stringify(xValues) + '</p>');
document.write('<p>xMax: ' + JSON.stringify(xMax) + '</p>');
document.write('<p>maxXObjects: ' + JSON.stringify(maxXObjects) + '</p>');
document.write('<p>maxXObject: ' + JSON.stringify(maxXObject) + '</p>');

Further information:

Solution 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');