Condense an if statement to find what range a value fits in

Question

So I'm trying to make a compass app for the Fitbit Ionic, it works but this piece of code makes me angry. I know there's a way to condense it but I can't figure out how. It is supposed to take an integer and tell me what is the corresponding cardinal direction.

It would look so much better if that if statement could be condensed. Any advice or solutions are greatly appreciated.

geolocation.watchPosition(function(position) {
var headingDir;
var headingDeg;
headingDeg = position.coords.heading ? position.coords.heading.toFixed(2) : 0

//This long boi
 if (headingDeg >= 22.5 & headingDeg < 67.5) {
  headingDir = "NE";
 } else if (headingDeg >= 67.5 & headingDeg < 112.5) {
  headingDir = "E"
 } else if (headingDeg >= 112.5 & headingDeg < 157.5) {
  headingDir = "SE"
 } else if (headingDeg >= 157.5 & headingDeg < 202.5) {
  headingDir = "S"
 } else if (headingDeg >= 202.5 & headingDeg < 247.5) {
  headingDir = "SW"
 } else if (headingDeg >= 247.5 & headingDeg < 292.5) {
  headingDir = "W"
 } else if (headingDeg >= 292.5 & headingDeg < 337.5) {
  headingDir = "NW"
 } else {
  headingDir = "N"
 };

})

All the conditions are returning different values, why do you want to compress them? — Krishna Prashatt, Jun 28 '18 at 06:21
I wanted to know if there was a better way to make this kind of if statement. — speedking456, Jun 28 '18 at 06:23

score 2 · Accepted Answer · edited Jun 28 '18 at 06:36

2

Because each range differs by the same amount (45), you can make an array for the direction strings, and then calculate the index of the direction string you want immediately:

const headingStrs = ['N', 'NE', 'E', 'SE', 'S', 'SW', 'W', 'NW', 'N'];
const getHeading = (deg) => headingStrs[Math.floor((deg + 22.5) / 45)];

console.log(getHeading(30)); // NE
console.log(getHeading(300)); // NW
console.log(getHeading(170)); // S
console.log(getHeading(22.5)); // NE
console.log(getHeading(15)); // N

edited Jun 28 '18 at 06:36

Drew Reese

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answered Jun 28 '18 at 06:27

CertainPerformance

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Not only very succinct, but O(1) instead of O(N). Kudos – Drew Reese Jun 28 '18 at 06:38
Works perfectly, just needed to add `parseFloat(deg)` rather than just `deg`, thx for the help! – speedking456 Jun 29 '18 at 01:31

score 0 · Answer 2 · answered Jun 28 '18 at 06:32

let headingDeg = 23;
let headingDir = '';

let headingObjArr = 
[
  {minDeg: 22.5, maxDeg: 67.5, value: 'NE'},
  {minDeg: 67.5, maxDeg: 112.5, value: 'E'},
  {minDeg: 112.5, maxDeg: 157.5, value: 'SE'}
]

headingDir = headingObjArr.find(function(element) {
  return headingDeg >= element.minDeg && headingDeg < element.maxDeg
});

console.log(headingDir.value)

You can store the condition and result as an object into an array, and using find to get the value

Condense an if statement to find what range a value fits in

2 Answers2