Swift for-loop "Expression type '[[String : String]]' is ambiguous without more context

Question

I am trying to access the following items from an Array of dictionaries and I have two problems (both are different approaches). The array of dictionaries is initialized as follows:

var testingArray = [[String: String]()]

testingArray.append(["name": "Ethiopia", "url": "localhost:8088"])
testingArray.append(["name": "Bugatti", "url": "localhost:8088"])
testingArray.append(["name": "Brazil", "url": "localhost:8088"])
testingArray.append(["name": "Jasmine", "url": "localhost:8088"])
testingArray.append(["name": "Hello", "url": "localhost:8088"])

The first method:

for (k,v) in testingArray {
    // code here
}

Won't run due to (which appears on the line the for loop is initialized):

"Expression type '[[String : String]]' is ambiguous without more context

The second method:

for indices in testingArray {
    for(k, v) in indices {
        print(indices.keys)
    }
}

returns the following:

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Ethiopia"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Ethiopia"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Bugatti"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Bugatti"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Brazil"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Brazil"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Jasmine"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Jasmine"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Hello"], _transform: (Function))

LazyMapCollection<Dictionary<String, String>, String>(_base: ["url": "localhost:8088", "name": "Hello"], _transform: (Function))

Here is pseudocode equivalent that I am trying to achieve:

for(int i = 0; i < sizeOfArray; i++ {
    print testingArray[i]."name"
    print testingArray[i]."url"
}

I have been scratching my head over this for days but I don't know swift and its idioms well enough to solve this alone, any help would greatly be appreciated (esp if we can figure out how to get #1 working).

In order to iterate a swift array with indices, see stackoverflow.com/a/24028458/958064 - Swift 3.0 adds an enumerated() method that would help OP here — sbauch
– sbauch, Commented Dec 14, 2017 at 20:12

jtbandes · Accepted Answer · 2016-04-01 23:33:46Z

7

I agree the error message is confusing/misleading. But for (k,v) in testingArray doesn't make sense, because testingArray is an array, not a dictionary. Its elements are dictionaries.

I think you're looking for something like this:

for obj in testingArray {
    print(obj["name"])
    print(obj["url"])
}

answered Apr 1, 2016 at 23:33

jtbandes

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4 Comments

刘哲诚 Over a year ago

thanks! It works like a charm. This is my first time using dictionaries so having a good grasp of the right syntax the first time is really important to me. It works, also just a side question, since dictionaries are unordered and non-enumerable, if I want to load from plist to a PickerView the easiest approach is to store all my dictionary kv pairs in an array yes?

jtbandes Over a year ago

If you need them to be in a specific order, yes, it'll be easiest to have them in an array. If each thing contains multiple properties (e.g. a "display name" and an "identifier") then it makes sense to use an array of dictionaries, as you've done in your example. (However, dictionaries are enumerable: in my example, you could do an inner loop like for (k, v) in obj { ... })

刘哲诚 Over a year ago

when you say enumerable, does that mean I can get the values from a dictionary within this function: pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {} like so: dictionary[row]["name"] ?

jtbandes Over a year ago

A dictionary itself is not indexable by integer row numbers. If you have an array of dictionaries called array, then you could do array[row]["name"], yes.

Mr Heelis · Accepted Answer · 2019-12-11 10:26:49Z

3

this works

for (k,v) in testingArray.enumerated() {
    for (_, element) in k.enumerated(){
       guard let elem = element.value as? [String: Any] else {
            continue
       }
       print elem["name"]
    }
}

edited Dec 11, 2019 at 10:26

answered Dec 11, 2019 at 10:12

Mr Heelis

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