比较字典值迅速

Question

I have an array of dictionaries of type

[["OptionId": 824, "QuestionId": 208],
["OptionId": 810, "QuestionId": 205],
["OptionId": 1017, "QuestionId": 257],
["OptionId": 0, "QuestionId": 201],
["OptionId": 0, "QuestionId": 199],
["OptionId": 0, "QuestionId": 200]]

I have iterated through these values and extracted the dictionaries values as

["OptionId": 824, "QuestionId": 208]
["OptionId": 810, "QuestionId": 205]
["OptionId": 1017, "QuestionId": 257]
["OptionId": 0, "QuestionId": 201]
["OptionId": 0, "QuestionId": 199]
["OptionId": 0, "QuestionId": 200]

Now, I want to get the "QuestionId" for all those "OptionId" which are 0. How can I compare the dictionary key-value to zero? Thanks in advance.

This is what I have tried so far:

for dictionary in arrayofDict {
    print(dictionary)
    if (dictionary["OptionId"] == 0) {
        print("option not selected")
    }
} 

Answer 1

You need to use filter on the array of dictionaries to get the dictionaries, where OptionId is 0, then use flatMap to get the corresponding non-optional QuestionId s.

let questionsDict: [[String:Any]] = [["OptionId": 824, "QuestionId": 208],["OptionId": 810, "QuestionId": 205], ["OptionId": 1017, "QuestionId": 257], ["OptionId": 0, "QuestionId": 201], ["OptionId": 0, "QuestionId": 199], ["OptionId": 0, "QuestionId": 200]]
let filtered = questionsDict.filter{($0["OptionId"] as? Int) == 0}.flatMap{$0["QuestionId"] as? Int} //contains 201,200,199

Answer 2

A "filter + map" operation can be done with a single flatMap call (avoiding the creation of an intermediate array). In your case:

let arrayofDict = [["OptionId": 824, "QuestionId": 208],
                 ["OptionId": 810, "QuestionId": 205],
                 ["OptionId": 1017, "QuestionId": 257],
                 ["OptionId": 0, "QuestionId": 201],
                 ["OptionId": 0, "QuestionId": 199],
                 ["OptionId": 0, "QuestionId": 200]]

let notSelected = arrayofDict.flatMap { $0["OptionId"] == 0 ? $0["QuestionId"] : nil }

print(notSelected) // [201, 199, 200]

Answer 3

尝试这个：

   arr.filter {return $0["OptionId"] == 0}.flatMap {return $0["QuestionId"]}return $0["QuestionId"]}

Answer 4

You can use filter as follows:

let searchPredicate = NSPredicate(format: "OptionId == %@",NSNumber.init(value: 0))
let filteredArray = arrayofDict.filter { searchPredicate.evaluate(with: $0) };
let result = filteredArray.flatMap{$0["QuestionId"]}