Delete and re-index dictionary in Swift

Question

Hi I have a dictionary of type:

1:[[12.342,34.234],[....,...],....] 2:[[......],[....]]....

Now I'd like to know if there are functions to delete specifics key and correspondents value, and a function to re-index it for examples if I delete the value correspondents to key 2 the key 3 should become the key 2 and so on.

if the key is a number, why not just use an array and access it by the index? — vikingosegundo, Jun 13 '17 at 17:31
them are arrays of coordinates and each array distinguishes a route @vikingosegundo — Valerio Schips, Jun 13 '17 at 17:33
why do you need an dictionary around them, that has int keys? — vikingosegundo, Jun 13 '17 at 17:34

score 1 · Answer 1 · answered Jun 13 '17 at 17:34

To delete a key and value, just do dict[key] = nil.

As for re-indexing, dictionary keys are not in any particular order, and shifting all the values over to different keys isn't how a dictionary is designed to work. If this is important for you, maybe you should use something like a pair of arrays instead.

score 1 · Answer 2 · answered Jun 13 '17 at 17:44

Dictionaries are not ordered. This means that "key 3" becoming "key 2" is not a supported scenario. If keys have been in the same order that you've inserted them, you've been lucky so far, as this is absolutely not guaranteed.

If you want ordering and your list of key/value pairs is small (a hundred or so is small), you should consider using an array tuples: [(Key, Value)]. This has guaranteed ordering. If you need something bigger than that or faster key lookup, you should find a way to define an ordering relationship between keys (such that you can say that one should always be after some other key), and use a sorted collection like this one.

thank you I thought to order the dictionary at the and using *.sorted{($1.key > $0.key)} function — Valerio Schips, Jun 13 '17 at 18:23

score 1 · Accepted Answer · answered Jun 13 '17 at 17:52

I think you need to use an Array, not a Dictionary

var elms: [[[Double]]] = [
    [[0.1],[0.2, 0.3]],
    [[0.4], [0.5]],
    [[0.6]],
]

elms.remove(at: 1) // remove the second element

print(elms)

[
    [[0.10000000000000001], [0.20000000000000001, 0.29999999999999999]],
    [[0.59999999999999998]]
]

Yes output values are slightly different from the original ones.

Delete and re-index dictionary in Swift

3 Answers3