How to swap values of an array? Javascript

Question

I am using Leaflet and I am trying to create a polyline and marker points but it gives opposite lat and long so I have to swap them. Creating a marker is easy because it only has one pair of lat and long but creating a polyline is complicated because has a lot of points.
Below is what I am currently using to swap lat and long for marker points.

var splitObj = objVal.toString().split("],[");
var latlng = splitObj.map(function(x)
    {
        var couple= (/\d+.\d+, \d+.\d+/g).exec(x).toString();
        var splitted = couple.split(", ");
        return "["+splitted[1]+","+splitted[0]+"]";
    });
latlng.join();

Result:

['[[a, b], [c, d], [e, f]]'] // this is the objVal
expectation:
['[[b,a], [d,c], [f,e]]']
reality:
['[b,a]']

Andy · Accepted Answer · 2022-03-23 04:35:39Z

3

map over the array it and, for each inner array, return a new array after swapping the elements around.

const data = [[124.432841, 8.3963], [124.496898, 8.3963], [124.571937, 8.40898]];

const result = data.map(arr => {
  return [arr[1], arr[0]];
});

console.log(result);

edited Mar 23, 2022 at 4:35

answered Mar 23, 2022 at 4:22

Andy

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7 Comments

jsN00b Over a year ago

Even simpler like so: const result = data.map(([la, lo]) => ([lo, la]));.

jsN00b Over a year ago

On second thought, I think in OP's question the data array is like so: const data = ['[124.432841, 8.3963], [124.496898, 8.3963], [124.571937, 8.40898]']. The whole inner-array is within quotes. So, it shows-up as a string & not an array.

Jane Doe Over a year ago

the results are [Array(2)] 0: Array(2) 0: "[" 1: "[" length: 2

jsN00b Over a year ago

To use this solution/method you need to pass it a nested-array of latitude, longitude values. Such as: [[124.432841, 8.3963], [124.496898, 8.3963], [124.571937, 8.40898]] <-- this is a nested array where the inner array are lat-long values. What exactly is your input - is it like the one above or is it like this: ['[[124.432841, 8.3963], [124.496898, 8.3963], [124.571937, 8.40898]]']. This is an array of just one element and that element is a string.

Andy Over a year ago

Is that an actual array, is it JSON? @JaneDoe. If it's JSON how are you parsing it? Your update makes less sense now because a and b are referring to variables, and not actual numbers.

|

jsN00b · Accepted Answer · 2022-03-23 07:21:28Z

Assuming the input is a string of nested-array-like values, the below solution may help in transforming/swapping latitude-longitude values.

Code Snippet

const inpVal = ['[[a, b], [c, d], [e, f]]'];

// helper method to strip first & last char of a string
const stripFirstLast = s => s.slice(1, s.length - 1);

// helper method to swap lat & longitutde values
const swapLatLon = ([lat, lon]) => [lon, lat];

// place holder to safe-keep value of input
const tmp = stripFirstLast(inpVal[0])
  .replaceAll('], ', '] | ')
  .split(' | ');

// calculate the result
const res = ["[" +
  tmp.map(
    x => '[' +
    swapLatLon(
      stripFirstLast(x).split(', ')
    ).join(', ') +
    ']'
  ).join(', ') +
  "]"
];

// console-log to validate/verify
console.log(
  'input: ', inpVal,
  '\nresult: ', res
);

Explanation

Comments inline explain the approach used.

Swap with actual values (and not string)

This is an almost-exact replica of Andy's solution/answer with only one change instead of handling the inner array as arr, the iterator directly accesses the lat & lon values. I think it makes the solution a little more easier to read.

// Previous solution where the orig data was not taken as a string
const swapLoLa = arr => arr.map(([lon, lat]) => [lat, lon]);
const orig = [[124.432841, 8.3963], [124.496898, 8.3963], [124.571937, 8.40898]];
console.log(
  'orig arr: ', orig,
  '\nswapped arr: ', swapLoLa(orig)
);

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