javascript array find highest value

Question

I have an array that I need to find the highest value of so when I apply it to a Highchart I can color the background if it exceeds some dynamic number a user inputs.

My code looks like this:

<div id="highest"></div>

var array = {
    data: [123, 234, 456, 789],
    data: [321, 654, 987],
    data: [963, 852, 741]
};

for (var i=0; i < array.data.length; i++){
    var m = Math.max.apply(Math, array.data);
    $('#highest').append('<div>'+m+'</div>');
}

all I get is the number

<div>963</div>
<div>963</div>
<div>963</div>

Don't you think it's weird that you're looping, but aren't doing anything with i? Use for in to loop over an object. And give unique keys — Ian
– Ian, Commented May 22, 2013 at 22:00
i is being used in the looping condition, so it's not quite doing nothing — Matt Berkowitz
– Matt Berkowitz, Commented May 22, 2013 at 22:01
Did you think it weird that your obects keys are all the same, overwriting each other -> Fiddle — adeneo
– adeneo, Commented May 22, 2013 at 22:01
yeah but it tells me I'm wrong no matter where I stick the i - I must be having an early case of Friday because I can't wrap my head around this — jbolanos
– jbolanos, Commented May 22, 2013 at 22:02
BTW, you don't need to supply the Math function as this, you can just use null. — RobG
– RobG, Commented May 22, 2013 at 23:58

Ian · Accepted Answer · 2013-05-23 05:07:53Z

4

Your array variable isn't an array([]), it is an object({}). You have multiple items in the object with the key data, but only one value per key is allowed.

So you have essentially written this:

var array = {
  data: [963, 852, 741]
};

Maybe you want something like this?

var array = [
  {data: [123, 234, 456, 789]},
  {data: [321, 654, 987]},
  {data: [963, 852, 741]}
];

var values = [];
for (var i=1; i < array.length; i++) {
  values.push.apply(values, array[i].data);
}
$('#highest').append('<div>' + Math.max.apply(Math, values) + '</div>');

or get rid of data entirely and just make it an array of arrays.

edited May 23, 2013 at 5:07

Ian

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answered May 22, 2013 at 21:59

loganfsmyth

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1 Comment

jbolanos Over a year ago

ok - when I applied your answer to my actual source array it actually worked - haha - go figure it was what I originally tried but my example array is wrong.

user1106925 · Accepted Answer · 2013-05-22 22:39:32Z

4

First make a proper nested array set. Then you can use .map() to do this:

var array = [
    [123, 234, 456, 789],
    [321, 654, 987],
    [963, 852, 741]
];

var maxVals = array.map(function(a) {
    return Math.max.apply(Math, a);
});

Or like this:

var maxVals = array.map(Function.apply.bind(Math.max, Math));

answered May 22, 2013 at 22:39

user1106925

3 Comments

Ian Over a year ago

That is so weird you posted this. I was literally about to make an answer. I've been trying to figure out how to do it the second way you have, and came up with the same thing. jsfiddle.net/SW7Ym . So weird.

Ian Over a year ago

Quick question - is there a reason you used Function.apply instead of Function.prototype.apply? I've always wondered, because I've seen people use Array.whatever instead of Array.prototype.whatever

user1106925 Over a year ago

@Ian: Just a quicker way to get to it. Since Function is a function, we don't need to go to the prototype. We could use isNaN.apply if we wanted. When people do Array.whatever, they're using a Firefox feature that can be easily shimmed in other browsers.

elclanrs · Accepted Answer · 2013-05-22 22:01:22Z

2

Well, that's not an array, it's an object with duplicated keys so you're just looping the last one that overrides all others.

Try this http://jsbin.com/olahuq/2/edit

var obj = {
  a: [123, 234, 456, 789],
  b: [321, 654, 987],
  c: [963, 852, 741]
};

var max = [];
for (var i in obj) {
  max.push(Math.max.apply(0, obj[i]));
}

$('#highest').append('<div>'+ max.join('</div><div>') +'<div>');

Altough you could just use an array of objects.

answered May 22, 2013 at 22:01

elclanrs

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2 Comments

jbolanos Over a year ago

unfortunately, I can't change the data object - it comes from a json dynamically generated by the server

elclanrs Over a year ago

Then I'd suggest you track the problem on the server and fix it there before going any further. Duplicated keys are wrong, by definition a key must be unique.

Ian · Accepted Answer · 2013-05-22 22:37:55Z

1

Not sure what you're trying to do here. That "array" variable is defined as an object. Object literals in JavaScript need unique keys. Your last array keyed by "data" in the "array" object is the only one that the interpreter picks up.

You might want this?

var data = [
  [123, 234, 456, 789],
  [321, 654, 987],
  [963, 852, 741]
];

for (var i=0; i < data.length; i++){
  var m = Math.max.apply(Math, data[i]);
  $('#highest').append('<div>'+m+'</div>');
}

edited May 22, 2013 at 22:37

Ian

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answered May 22, 2013 at 22:06

AndersDJohnson

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Comments

user428517 · Accepted Answer · 2013-05-22 22:11:53Z

0

You are using multiple keys with the same name, which isn't valid JavaScript (well, the code may still run, but you won't get the results you're expecting). This is easy to fix, though—just use an array instead:

var arr = [
    [123, 234, 456, 789],
    [321, 654, 987],
    [963, 852, 741]
];

for (var i=0; i < arr.length; i++){
    var m = Math.max.apply(Math, arr[i]);
    $('#highest').append('<div>'+m+'</div>');
}

You could do this with an object, but I don't see any reason to, unless you're reading this data from a service or something and can't change its format.

edited May 22, 2013 at 22:11

answered May 22, 2013 at 22:05

user428517

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2 Comments

user428517 Over a year ago

anyone want to explain the downvote? i try to address the spirit of the question, not give literal answers for every question asked.

jbolanos Over a year ago

you are [ containing [ in an array

Marcello di Simone · Accepted Answer · 2019-05-16 08:48:45Z

0

I just want to add another even more reduced way.

var obj = {
  a: [123, 234, 456, 789],
  b: [321, 654, 987],
  c: [963, 852, 741]
};
var max = Math.max.apply(0, [].concat.apply([], Object.values(obj)));

This however might be to obfuscated to be used in production code, I'd rather use reduce instead for better readability.

var max = Object.values(obj)
      .reduce((a, d) => a.concat(d), [])
      .reduce((p, c) => Math.max(p, c));

Finally you can also replace the latter reduce with a sort method:

var max = Object.values(obj)
      .reduce((a, d) => a.concat(d), [])
      .sort((l, r) => l - r)
      .pop();

edited May 16, 2019 at 8:48

answered May 16, 2019 at 8:41

Marcello di Simone

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