Math.Max returning Nan on array after creating array of numbers Javascript

Question

I created an array in Javascript that should be all numbers. When I use Math.max on it, the function returns NaN. I am stumped. First, I know the documentation says Math.max returns NaN when one of the arguments cannot be converted to a number, so I think that is happening. I cannot understand what that is.

Here d is an array of objects. The objects are key-value pairs. I want to put all the values of each object in the d array into one new array and then find the max. Here is how I make my new array valsarr:

var valsarr = [];
d.map(function(row){ 
    Object.keys(row).forEach(function(key) {
        row[key] = Number(row[key]);
        valsarr.push(Number(row[key]));
    });
});

I know using Number twice is redundant, but I added the second to be extra careful. I tried parseInt and + in its place and had the same result. Then I try to obtain the max of that array and print:

var mymax = Math.max.apply(Math, valsarr)
console.log(mymax);

It prints NaN As part of the debugging process, I tried filtering the array to find non-numbers in it, but I get nothing. My code for that task could be faulty too, however. Here it is:

function isNotNumber(value) {
    return (typeof(value) !== "number");
}
var badarr = valsarr.filter(isNotNumber);
console.log('Filtered Array\n', badarr);

It prints an array of length 0. I believe that means it found no non-number values in the array.

Two more notes: The original data in d contains thousands of values. It comes from .csvs. So I don't want to hunt through all the values to find ones that are not numbers. I can easily see the original d object and the valsarr array do have numbers in them. Second, it works when I load in one of the .csvs I am using but not any of the others.

But again, with any of the .csvs, both d and valsarr have at least some numbers in them when I scan through them to check, so the first code block is doing something, at least every time.

Any help would be greatly appreciated.

This will filter non-numbers: valsarr.filter(v => ! isNaN(v)); — fubar
– fubar, Commented Feb 16, 2018 at 2:56
to find non-numbers use var badarr = valsarr.filter(isNaN) — Kosh
– Kosh, Commented Feb 16, 2018 at 2:56

HMR · Accepted Answer · 2018-02-16 05:19:00Z

Math.max takes several arguments, not an array. You can use spread (ES7)

Math.max(...[1,2,3,4])

Or you can use apply:

Math.max.apply(null,[1,2,3,4])

Make sure to take out anything from the array that isn't a number as laxydeveloper suggested:

Math.max.apply(null,array.filter(x=>!isNaN(x))

In your code it would look like this:

var d = [
  {p:"hello"},
  {d:2},
  {q:7},
  {other:1,highest:10},
  {q:7}
];
var highest = Math.max.apply(
  null,
  d.map(
    row=>
      Object.keys(row).map(
        key=>
          Number(row[key])
      )
  ).reduce(//flatten array of arrays [[1,2],[2,3]] to [1,2,3,4]
    (all,item)=>all.concat(item),
    []
  ).filter(//take out all that are not numbers
    x=>!isNaN(x)
  )
);
console.log("highest:",highest);

If you want to know the index and key of the object having the highest value you can do this:

var d = [
  {p:"hello"},
  {d:2},
  {q:7},
  {other:1,highest:10},
  {q:7}
];
//get highest value,index and the key
const [highestVal,highestKey,highestIndex] = d.map(
  (item,index)=>
    Object.keys(item).reduce(
      (all,key)=>all.concat([[item[key],key,index]]),//val,key,index
      []
    )
).reduce(
  (highest,item)=>{
    return item.reduce(
      (highest,[val,key,index])=>{
        return (val>highest[0])
          ? [val,key,index]
          : highest
      },
      highest
    )
  },
  [-Infinity,undefined,undefined]
);
console.log(
  "highest value:",highestVal,
  "highest object",d[highestIndex],
  "highest key of that object:",highestKey
);

Mike K · Accepted Answer · 2018-02-16 02:53:17Z

0

Maybe you could cheat a bit, and try to find the badly behaved value by checking right at the time that you set the value:

Object.keys(row).forEach(function(key) {
    row[key] = +row[key];
    valsarr.push(row[key]);
    if (Math.max(row[key]) !== row[key]) {
        console.log(row);
    }
}

and then you can see the offending row...

answered Feb 16, 2018 at 2:53

Mike K

6485 silver badges9 bronze badges

Comments

lazydeveloper · Accepted Answer · 2018-02-16 03:08:54Z

0

you can use filter function for removing NaN from array.

  var valsarr = [];//initialize data in array 
  var result=  valsarr.filter(v => ! isNaN(v));

answered Feb 16, 2018 at 3:08

lazydeveloper

97111 silver badges23 bronze badges

Comments

th3n3wguy · Accepted Answer · 2018-02-16 04:55:25Z

You should be able to run the Math.max() function on the valsArray that I create in my code below without any problems.

// Your code:
/*var valsarr = [];
d.map(function(row){ 
  // This is what you were doing, but you weren't actually returning anything back to the map function, so you weren't creating anything new on the `d` setup, as well as you weren't assigning the return value of the .map() function to anything.
  Object.keys(row).forEach(function(key) {
    row[key] = Number(row[key]);
    valsarr.push(Number(row[key]));
  });
});*/

// Creating a mock set of data for "d", since you didn't provide it.
var d = [
 { a: '1', b: '2', c: '3' },
 { a: '1', b: '2', c: 'test' }, // This should fail.
 { a: '1', b: '2', c: '3' },
 { a: '1', b: '2', c: '3' },
 { a: '1', b: '2', c: '3' }
]

// This is what I think you are trying to do:

// I am doing this concat.apply() method because the Object.values() inside of the .map() method creates a new Array with the values, so we need to concatenate all of them together 
var valsArray = [].concat.apply([], d.map((row) => {
  return Object.values(row)
    .filter((val) => {
      console.log('Trouble-causing row:', isNaN(parseInt(val)), row, val);
      return !isNaN(parseInt(val));
    })
    .map((val) => parseInt(val))
}));

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