Is there a way of reading from sub arrays? - arrays

Question

I am currently building an iOS application that stores user added products using Google Firestore. Each product that is added is concatenated into a single, user specific "products" array (as shown below - despite having separate numbers they are part of the same array but separated in the UI by Google to show each individual sub-array more clearly)
I use the following syntax to return the data from the first sub-array of the "products" field in the database
let group_array = document["product"] as? [String] ?? [""]
if (group_array.count) == 1 {
let productName1 = group_array.first ?? "No data to display :("`
self.tableViewData =
[cellData(opened: false, title: "Item 1", sectionData: [productName1])]
}
It is returned in the following format:
Product Name: 1, Listing Price: 3, A brief description: 4, Product URL: 2, Listing active until: 21/04/2021 10:22:17
However I am trying to query each of the individual sections of this sub array, so for example, I can return "Product Name: 1" instead of the whole sub-array. As let productName1 = group_array.first is used to return the first sub-array, I have tried let productName1 = group_array.first[0] to try and return the first value in this sub-array however I receive the following error:
Cannot infer contextual base in reference to member 'first'
So my question is, referring to the image from my database (at the top of my question), if I wanted to just return "Product Name: 1" from the example sub-array, is this possible and if so, how would I extract it?

Answer 1

I would reconsider storing the products as long strings that need to be parsed out because I suspect there are more efficient, and less error-prone, patterns. However, this pattern is how JSON works so if this is how you want to organize product data, let's go with it and solve your problem.
let productRaw = "Product Name: 1, Listing Price: 3, A brief description: 4, Product URL: 2, Listing active until: 21/04/2021 10:22:17"
First thing you can do is parse the string into an array of components:
let componentsRaw = productRaw.components(separatedBy: ", ")
The result:
["Product Name: 1", "Listing Price: 3", "A brief description: 4", "Product URL: 2", "Listing active until: 21/04/2021 10:22:17"]
Then you can search this array using substrings but for efficiency, let's translate it into a dictionary for easier access:
var product = [String: String]()
for component in componentsRaw {
let keyVal = component.components(separatedBy: ": ")
product[keyVal[0]] = keyVal[1]
}
The result:
["Listing active until": "21/04/2021 10:22:17", "A brief description": "4", "Product Name": "1", "Product URL": "2", "Listing Price": "3"]
And then simply find the product by its key:
if let productName = product["Product Name"] {
print(productName)
} else {
print("not found")
}
There are lots of caveats here. The product string must always be uniform in that commas and colons must always adhere to this strict formatting. If product names have colons and commas, this will not work. You can modify this to handle those cases but it could turn into a bowl of spaghetti pretty quickly, which is also why I suggest going with a different data pattern altogether. You can also explore other methods of translating the array into a dictionary such as with reduce or grouping but there are big-O performance warnings. But this would be a good starting point if this is the road you want to go down.
All that said, if you truly want to use this data pattern, consider adding a delimiter to the product string. For example, a custom delimiter would greatly reduce the need for handling edge cases:
let productRaw = "Product Name: 1**Listing Price: 3**A brief description: 4**Product URL: 2**Listing active until: 21/04/2021 10:22:17"
With a delimiter like **, the values can contain commas without worry. But for complete safety (and efficiency), I would add a second delimiter so that values can contain commas or colons:
let productRaw = "name$$1**price$$3**description$$4**url$$2**expy$$21/04/2021 10:22:17"
With this string, you can much more safely parse the components by ** and the value from the key by $$. And it would look something like this:
let productRaw = "name$$1**price$$3**description$$4**url$$2**expy$$21/04/2021 10:22:17"
let componentsRaw = productRaw.components(separatedBy: "**")
var product = [String: String]()
for component in componentsRaw {
let keyVal = component.components(separatedBy: "$$")
product[keyVal[0]] = keyVal[1]
}
if let productName = product["name"] {
print(productName)
} else {
print("not found")
}