Map numbers to other numbers with interpolation in Javascript

Question

I have a dataset with a volume for a given surface elevation of an irregular basin. For example:

cm      kL
11870 : 6043453
11871 : 6053522
11872 : 6063591
11873 : 6073674
11874 : 6083767
(...1550 rows)

cm is a series that always increments by one; The associated kL values are irregular but always increase and are never duplicated. The mapping never changes and it can be loaded/stored in any convenient format.

Does Javascript have a simple way to convert between cm and kL? Ideally with linear interpolation in both directions. Ultimately I am looking for this functionality:

cm_to_kL(11872.2); //Expect 6065607.6
kL_to_cm(6065600); //Expect 11872.199

No, there really no basic data structure that allows two way mapping alone. So you'd need to write your own. (Also it looks like array of "kL" values is all you need with couple lines to do linear interpolation between subsequent values or indexes - O(1) for cm_to_kL, O(log n) for kL_to_cm) — Alexei Levenkov
– Alexei Levenkov, Commented Mar 9, 2022 at 23:19
Hi there, maybe I don't understand well what you're asking for...you need to convert from one unit to other or you have both unit yet and you need to find the corresponding one starting from other? I.e. I know both cm and kl yet, and I want a function that find the corresponding cm if I insert kl as parameter and vice versa? — Gianfabio Pezzolla
– Gianfabio Pezzolla, Commented Mar 9, 2022 at 23:49
Unless this is an assignment, I'd suggest using an equation to convert between the two units. But I'm not sure if "cm" should be cm^3, or if kL should be kilo-litre or some other measure. — David Thomas
– David Thomas, Commented Mar 10, 2022 at 0:13
@DavidThomas the data seem to be just empirical (my guess it is lake depth to total volume, measured in cm and Kilo Liters correspondingly), no formula would exist for that. — Alexei Levenkov
– Alexei Levenkov, Commented Mar 10, 2022 at 0:23

Samuli Hakoniemi · Accepted Answer · 2022-03-10 00:12:13Z

1

I wrote an example of how to start solving this problem. Like already mentioned, there are no internal functionality for interpolating or handling such structures, but you need to write your own logic.

I have to admit I'm not an expert what comes to math (+ it's 2am here, but this question got me interested in :D).

I hope this helps you at least to get started:

const data = {
  11870 : 6043453,
  11871 : 6053522,
  11872 : 6063591,
  11873 : 6073674,
  11874 : 6083767,
};

const cm_to_kL = (val) => {
    const cm_ref = Math.floor(val);
    const factor = parseFloat((val % cm_ref).toFixed(5));
    const lower = data[cm_ref];
    const higher = data[cm_ref + 1];

    if (isNaN(lower) || isNaN(higher)) {
        throw Error('Data entry point not found');
    }
    
    const result = lower + ((higher - lower) * factor);

    if (isNaN(result)) {
        throw Error('Incorrect data provided');
    }

    return result;
};

const kL_to_cm = (val) => {
    const [cm, kL] = Object.entries(data).find(([k, v]) => val < v);

    if (isNaN(cm) || isNaN(kL)) {
        throw Error('Data entry point not found');
    }
    
    const lower_cm = cm - 1;
    const lower_kL = data[lower_cm];
    const diff = (val - lower_kL) / (kL - lower_kL);

    const result = parseFloat((lower_cm + diff).toFixed(5))

    if (isNaN(result)) {
        throw Error('Incorrect data provided');
    }

    return result; 
};

console.log('11872.2',
    cm_to_kL(11872.2),
);

console.log('6065600',
    kL_to_cm(6065600),
);

answered Mar 10, 2022 at 0:12

Samuli Hakoniemi

19.1k1 gold badge64 silver badges79 bronze badges

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

1 Comment

NiaBassey Over a year ago

The way I read it it looks like I need to lookup the exact kL value for the floor of the matching cm key as well as the value for the next key, then use the cm mantissa to interpolate between the "lower" & "higher" kL values. For kL_to_cm the only difference is the lookup, but since it always increases we just look for the first value greater than the lookup value as well as the key immediately below it. This is pretty much what I expected, it just felt like surely there was some kind of map function to at least lookup the nearest values and keys. Thanks for the comments!

EzioMercer · Accepted Answer · 2022-03-10 00:07:18Z

0

Yes of course JS have to do what you need! You can create 2 Maps from your given array, one for cm to kL and another for kL to cm. Create two functions for them cm_to_kL and kL_to_cm to gat value from Maps after this you can easily get elements with O(1) complexity

edited Mar 10, 2022 at 0:07

answered Mar 9, 2022 at 23:56

EzioMercer

2,1482 gold badges11 silver badges30 bronze badges

3 Comments

EzioMercer Over a year ago

@NiaBassey if you need exact code example, then please edit your answer and show in which format you will get input data

David Thomas Over a year ago

As a general recommendation I'd suggest that an answer should always offer a code example to demonstrate implementation (but it is, of course, your call).

EzioMercer Over a year ago

@DavidThomas I always try to add some code but in this situation I couldn't understand what is the input, 2 arrays with same length or 1 object with keys and values so I decided to wait answer, and then give an algorithm to solve the problem

Collectives™ on Stack Overflow

Map numbers to other numbers with interpolation in Javascript

2 Answers 2

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related