# nrkno/valg-valgomat-algoritme

The algorithm used to calculate distance between sets of positions for NRKs Valgomat
DonnyCraft1 and mollerse Fix typo 'betwen'
```Jeg kommer hit fra NRKbeta-artikkelen, som forresten var ganske interessant. Jeg fant en typo i README.md. Det er kanskje litt mye å forke hele repoet bare for én bokstav, men nå er det gjort 😀

***

*I found a typo in README.md, here is a pull request just for ONE letter. I guess I could just submit an issue, but it's too late now..*```
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# Valgomat algorithm

Calculate the distance between two sets of positions.

Calculates the distance between two sets of positions. Mostly used to calculate the distance between various party positions and a voter position.

## Usage

The simple case is comparing to sets of positions.

```import { distance } from "@nrk/valg-valgomat-algoritme";

let partyPositions = {
"1": { value: 1 },
"2": { value: -1 }
};

let voterPositions = {
"1": { value: -2 },
"2": { value: 2 }
};

let d = distance(partyPositions, voterPositions); // => 0.25```

The module also comes with a function to compare many positions to one position.

```import { distanceMap } from "@nrk/valg-valgomat-algoritme";

let partyAPositions = {
"1": { value: 1 },
"2": { value: -1 }
};

let partyBPositions = {
"1": { value: 2 },
"2": { value: -2 }
};

let partyPostitions = {
partyA: partyAPositions,
partyB: partyBPositions
};

let voterPositions = {
"1": { value: 0 },
"2": { value: -2 }
};

let optionalWeights = {
partyA: 1.0,
partyB: 1.0
};

let distances = distanceMap(voterPositions, partyPositions, optionalWeights); // => { "partyA": 0.75, "partyB": 1.0 }```

## API

`import { distance, distanceMap } from "@nrk/valg-valgomat-algoritme";`

### let d = distance(positionsA, positionsB);

Accepts two sets of positions and returns the distance between them.

Positions are given in the form of sets:

```{
[statement: string]: { value: number }
}```

Where `value` is in the interval `[-2.0, 2.0]`

Output will be a number in the interval `[0.0, 1.0]` where `0.0` is the largest possible distance and `1.0` is the smallest possible distance (iow. identical).

If a `value` is close to `0` (currently defined as `+/-0.3`), it will be handled as a special case and given twice the distance to a value that is not close to `0`. I.e. the distance between `0.1` and `1.0` will become `1.8`.

This is done to more accuratly represent the situation where a party, voter or model party is taking a position close to `0`. Such a position is considered as a completely unknown position, it could go either way when one is forced to consider it. Comparing moderate positions (`-1/1`) to this unknown position would be unreasonably favorable if we hadn't implemented this mechanism.

### let distances = distanceMap(positionsA, positionsMap, optionalWeights = {});

Accepts a set of positions and a map of many sets of positions and returns a map of the distances between a position in the position map and the first position. Optionally provide weights for keys in `positionsMap`, will multiply `distance` with `weight` for that key.

This is useful if you want to calculate the distance between one set of positions and many sets of positions. For instance between all parties and a single voter.

Output will be a map from the keys in the positionsMap and the distance to the given position.

## Extra

See validation or tools for documentation on some of the extra features of this pacakge.

## Installation

`npm install @nrk/valg-valgomat-algoritme`

## Glossary

• Position = Standpunkt
• Statement = Påstand
• Party = Parti
• Voter = Velger

## A note on codestyle

This module uses default configuration of Prettier.

This module uses CommonJS/Node-style `require` for broadest possible ecosystem-compatbility without additional compile-steps.

This module uses a fairly modern flavor of JavaScript and will require compilation if it is to be used with older runtimes.