Reverse Array of coordinates in swift 4 - arrays

Question

I am trying to reverse an array of coordinates. I have this array:
[
[
9.211615025997162,
44.30419567985762
],
[
9.21164184808731,
44.30412081929745
],
[
9.21165257692337,
44.304053636662175
],
[
9.211606979370117,
44.3038789614507
],
[
9.211572110652924,
44.30381945658962
],
[
9.211539924144745,
44.30378874437967
],
[
9.211507737636566,
44.30376187118276
],
[
9.211564064025879,
44.30377530778277
],
[
9.211574792861937,
44.30374075651943
],
[
9.211574792861937,
44.30371388330059
],
[
9.211574792861937,
44.30369852717
],
[
9.21154797077179,
44.303665895379176
],
[
9.211513102054596,
44.303650539236024
],
[
9.211429953575134,
44.30358911462331
],
[
9.211349487304688,
44.30355840229286
],
[
9.211271703243256,
44.303537287556324
],
[
9.21117514371872,
44.30349505806051
],
[
9.211151003837585,
44.303473943301235
],
[
9.211126863956451,
44.30342979423452
],
[
9.211145639419556,
44.30339908182071
],
[
9.211183190345764,
44.303368369390846
],
[
9.211223423480988,
44.30331846165803
],
[
9.211242198944092,
44.30327623200479
],
[
9.211177825927734,
44.30325895622883
],
[
9.211030304431915,
44.303228243725634
],
[
9.210925698280334,
44.30321096793552
],
[
9.210874736309052,
44.303197531206386
],
[
9.210831820964813,
44.303197531206386
],
[
9.21075403690338,
44.303197531206386
],
[
9.21068161725998,
44.3031994507393
],
[
9.210577011108398,
44.3031994507393
],
[
9.210509955883026,
44.303207128870355
],
[
9.210440218448639,
44.303207128870355
],
[
9.210370481014252,
44.30322632419366
],
[
9.2102712392807,
44.30324743904202
],
[
9.210190773010254,
44.30328199059568
],
[
9.210112988948822,
44.30328391012582
],
[
9.210059344768524,
44.303297346835215
],
[
9.209954738616943,
44.30332422024474
],
[
9.209901094436646,
44.303339576473235
],
[
9.209868907928467,
44.303349174114
],
[
9.209858179092407,
44.30338372560779
],
[
9.209791123867035,
44.30340292087333
],
[
9.209697246551514,
44.30342595518367
],
[
9.209648966789246,
44.3034509090097
],
[
9.209606051445007,
44.30351809233474
],
[
9.209579229354858,
44.30355840229286
],
[
9.209581911563873,
44.3035852755829
],
[
9.209622144699097,
44.30355840229286
],
[
9.20967847108841,
44.30355648277167
],
[
9.209697246551514,
44.30354112659989
]
]
And I would like to reverse the coordinates, which are right now in Long-Lat to Lat-Long thus reversing the whole array or each item in the array would do the job here. I have been stuck trying to make it work, trying things like arrayOfCoords.reversed() and .reverse() to no avail. So how can I do this?

Answer 1

There may be a more elegant/efficient way to do this, but I'd look at using compactMap:
let testArray = [[1.123,2.22], [3.11, 4.0], [5.21, 6.19]]
print(testArray)
[[1.123, 2.22], [3.11, 4.0], [5.21, 6.19]]
let flippedElementArray = testArray.compactMap { $0.count > 1 ? [$0[1], $0[0]] : nil }
print(flippedElementArray)
[[2.22, 1.123], [4.0, 3.11], [6.19, 5.21]]
The $0.count > 1 check just makes sure you have at least 2 elements so you don't get a bounds error. If not, the closure returns nil for that element, which will be filtered out by compactMap. Otherwise, it returns a new array element consisting of the second element followed by the first element. All of those elements are stored in the final mapped array (flippedElementArray).

Answer 2

arrayOfCoords.map{ Array($0.reversed()) }
I'm assuming you want to reverse each coordinate pair, but keep the pairs themselves in the original order. Since you have an array of arrays, you have to do the operation on each sub-array separately. And reversed() returns a ReversedCollection instead of an Array so you have to re-initialize it into an array to use it properly.