swift - Using `flatMap().filter().map()` together on a multidimensional array -

i use following method find identifier isbooltrue==true nested array (screenshot of array , data structure below)

func extractidentifiers(mainarray: [mainitem]) -> [int]? {     var selected = [int]()     mainarray.foreach { element in         let integers = element.innerarray?.filter({ $0.isbooltrue }).map {             int($0.identifier)!         }         if !(integers?.isempty ?? true) {             selected += integers!         }     }      return selected.isempty ? nil : selected } 

question: possible use sort of chaining flatmap().filter().map() produce same result [int]?, able eliminate use of mainarray.foreach , conditional checks selected.isempty , integers?.isempty?

note: need within above method extractidentifiers, below find data , structure play around, screenshot of array.

thanks in advance!

structure & data:

struct inneritem {     let identifier: string     var isbooltrue: bool } struct mainitem {     var innerarray: [inneritem]? } let str = "[{\"innerarray\":[{\"identifier\":\"0\",\"isbooltrue\":true},{\"identifier\":\"1\",\"isbooltrue\":false}]},{\"innerarray\":[{\"identifier\":\"3\",\"isbooltrue\":true},{\"identifier\":\"4\",\"isbooltrue\":false}]},{\"innerarray\":null}]"  let data = str.data(using: string.encoding.utf8)! let json = try jsonserialization.jsonobject(with: data, options: .allowfragments) as? [[string : any]] var mainarray = [mainitem]() json!.foreach { dict in     if let array = dict["innerarray"] as? [[string: any]] {         let innerarray = array.map {             inneritem(identifier: $0["identifier"] as! string, isbooltrue: $0["isbooltrue"] as! bool)         }         mainarray.append(mainitem(innerarray: innerarray))     } } 

tests & output

var selected: [int]? // fill array `identifier`  // test1 selected = extractidentifiers(mainarray: mainarray) // output: [0, 3]  // test2 mainarray[0].innerarray![0].isbooltrue = false selected = extractidentifiers(mainarray: mainarray) // output: [3]  // test3 mainarray[1].innerarray![0].isbooltrue = false selected = extractidentifiers(mainarray: mainarray) // output: nil 

my approach flatten nested array array of dictionaries using double flatmap, filter object true value , @ last use map "identifier" value.

let result = data.flatmap { $0.flatmap { $0.value } } // line flatten 1 level         .filter { $0["isbooltrue"] == true }         .map { $0["identifier"] }  print(result) // output ["0", "3"] 

note: have better understanding on output, try print line line