Simple algorithm

Question

Can someone more intelligent than me please solve this simple math conversion that I need to accomplish within javascript.

If I have an ordered array of numbers say...

var values = [99, 101, 102, 103, 104];
var low = 99;
var high = 104;

...and I need the highest value in the array to be pushed to a new array as the value 1, and the second highest value to be pushed to the new array as 2, etc., so the new array is...

var newArray = [1, 2, 3, 4, 6];

I can make a hack version that works but I need a solution that will work on arrays with diverse number values. Appreciate the help!

what is the logic behind pushing 1 instead of 104. If there is no reason then simply Array.fill will work — brk
– brk, Commented Jun 5, 2018 at 17:13

Nina Scholz · Accepted Answer · 2018-06-05 17:27:59Z

2

You could map the delta of high value and value plus one and reverse the array.

var values = [99, 101, 102, 103, 104],
    low = 99,
    high = 104,
    result = values
        .map(v => high + 1 - v)
        .reverse();
 
console.log(result);

edited Jun 5, 2018 at 17:27

answered Jun 5, 2018 at 17:21

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Asons Over a year ago

Small question, with a callback function one can also get the index and the array, is that possible with the arrow function?

Nina Scholz Over a year ago

the callback has the same signature for arrow functions as for standard functions, like (item, index, array) => ....

Asons Over a year ago

Thank you very much for that ... I didn't understand to enclose the parameters with parenthesis.

Nina Scholz Over a year ago

maybe you have a look here, too: arrow functions

Asons Over a year ago

Thanks again ... actually been at that page before but obviously missed (read lazy :) the line // Parentheses are optional when there's only one parameter name. Never had the time to dig deeper into all these new stuff. They weren't available when I started coding 25 years ago :)

Gary · Accepted Answer · 2018-06-05 17:49:23Z

2

May be something like this

var values = [99, 101, 102, 103, 104];
var low = 99;
var high = 104;

var newOutputArr = [];
newOutputArr.push(1);


for (var j=values.length - 2; j>=0; j--) {
  var cal = Math.abs(values[j] - high) + 1;
  newOutputArr.push(cal);
}

console.log(newOutputArr);

Hope this helps!

edited Jun 5, 2018 at 17:49

Gary

14k18 gold badges54 silver badges73 bronze badges

answered Jun 5, 2018 at 17:17

zenwraight

1,9881 gold badge12 silver badges14 bronze badges

Comments

Asons · Accepted Answer · 2018-06-05 17:53:32Z

2

With map and reverse, you could subtract each value from the first and then add 1

Stack snippiet

var values = [99, 101, 102, 103, 104];

var new_values = values.reverse().map(function (val, idx, arr) {
    return (arr[0] - val + 1);
})

console.log(new_values);

Or with an arrow function (this won't work with IE though)

var values = [99, 101, 102, 103, 104];

var new_values = values.reverse().map((val,idx,arr) => arr[0] - val + 1);

console.log(new_values);

edited Jun 5, 2018 at 17:53

answered Jun 5, 2018 at 17:27

Asons

87.7k12 gold badges119 silver badges175 bronze badges

1 Comment

J. Pena Over a year ago

Thanks so much guys! Really appreciate it!

Cory Kleiser · Accepted Answer · 2018-06-05 19:12:18Z

0

I would use Array.prototype.reduce. And forgo the use of the low and high variables. Then you can use any sorted array. Something like this:

const values = [99, 101, 102, 103, 104, 108, 199, 200, 234, 235];

const newArray = values.reduce( (i, v, a, b) => {
  
  if(a === 0) i.push(1)
  else i.push(i[a - 1] + v - b[a-1])
  
  return i
    
}, []);

console.log(newArray)

edited Jun 5, 2018 at 19:12

answered Jun 5, 2018 at 17:51

Cory Kleiser

2,0332 gold badges16 silver badges27 bronze badges

Comments

Redu · Accepted Answer · 2018-06-09 18:26:26Z

0

Just a single pass of .reduceRight() is sufficient.

var values = [99, 101, 102, 103, 104],
    low    = 99,
    high   = 104,
    result = values.reduceRight((r,v) => r.concat(high-v+1), []);
console.log(result);

answered Jun 9, 2018 at 18:26

Redu

26.3k6 gold badges61 silver badges84 bronze badges

Collectives™ on Stack Overflow

Simple algorithm

5 Answers 5

5 Comments

Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

5 Comments

Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related