Swift: Dictionary of Dicitionaries, cannot get subscript - swift

Question

I've looked at other subscript issues here and I don't think they match my problem. I have a dictionary of dictionaries - Dictionary[String:Dictionary[String:String]]
In an extension I want to loop through all the values (Dictionary[String:String] and retrieve one of the values.
So I wrote this:
for dictNEO in Array(self.values) {
print(dictNEO)
print(type(of: dictNEO))
print(dictNEO["approachDate"])
}
and am getting this error on the last print line: Value of type 'Value' has no subscripts
Here's the first two print lines:
["nominalDist": "\"13.58 ", "approachDate": "\"2020-Feb-01 08:18 ± < 00:01\"", "minimumDist": "\"13.58 ", "diameter": "\"92 m - 210 m\"", "name": "\"(2017 AE5)\""]
Dictionary<String, String>
So I am confused as to why it is telling me it has no subscripts when it sees the type of as a Dictionary.

Answer 1

You have written this as an extension to Dictionary if I understand you correctly and that means that self is generic and defined as Dictionary<Key, Value> and not to you specific type so in your for loop you are looping over an array of [Value].
So you need to typecast Value before accessing it as a dictionary
if let dictionary = dictNEO as? [String: String] {
print(dictNEO["approachDate"])
}
but since it makes little sense to have an extension to Dictionary where you access a specific key it would be better to write it as a function. Since the dictionary is well defined now there is no issue with the last print
func printValuesForSubKey(_ key: String, _ dict: [String: [String: String]]) {
for (dictNEO) in dict.values {
print(dictNEO)
print(type(of: dictNEO))
print(dictNEO[key])
}
}
Note, I don't have an explanation why type(of:) recognises it as [String: String]

Answer 2

The code snippet doesn't work because values property is a collection of collections and with Array(values) you create a collection of collection of collections. In short, instead going down the code goes up and creates new collection level.
Solution with a Higher order function map:
self.values.map { print(type(of: $0)); $0["approachDate"] }
Solution with For-In Loop
for dictNEO in self.values {
print(dictNEO)
print(type(of: dictNEO))
print(dictNEO["approachDate"])
}