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How to convert string which have array and string elements inside it, to fetch each element from the array in Kotlin [Android]

My output looks like this :
["Floor 0","Floor 1","Floor 2"]
It comes as a string. But I want to fetch each element of this array. How can I do this using Kotlin ?

implement this library Gson
you can use it like this
val text = "[\"Floor 0\",\"Floor 1\",\"Floor 2\"]"
val array = Gson().fromJson(text, ArrayList::class.java)
array.forEach {
Log.e(TAG, "onCreate: it $it")
}

Just use regular expressions to create a match for each CharSequence between the double quotes. As you want to use only the values between the quotes, you can extract the first index group values. The following code snippet does what you are asking for in Kotlin:
val str = "[\"Floor 0\",\"Floor 1\",\"Floor 2\"]"
val pattern = Regex( "\"(.*?)\"")
val fetched_elements = pattern.findAll(str).map {
it.groupValues[1]
}.toList()
// creates the list: [Floor 0, Floor 1, Floor 2]
Use also this RegExr example to explore this in detail with explanation.

If your internal strings aren't allowed to have commas, you could do it with a split function to convert it into a list:
var lst = str.replace("\"", "").split(",")
If your internal strings can have trailing whitespace, this would be better:
var lst = str.replace("\"", "").split(",").map { it.trim() }
In the above code lines, the replace function removes the quotes surrounding each internal string; the split separates the string at each comma; and the trim function removes any surrounding whitespace characters.
If your internal strings can contain commas, you're better off learning about and using regular expressions as mentioned in another answer.

How to make an array of arrays in kotlin?

I have an array of userIDs, which contains specific users from a certain group.
{userID1,userID2}
val userIDArrayList: ArrayList<String> = ArrayList()
userIDArrayList.add(userID1)
userIDArrayList.add(userID2)
I want to make a master array which contains several different user arrays.
[{userID1, userID2}, {userID3, userID4}]
How can I do that in kotlin?

mutableListOf(mutableListOf("yourobject"),mutableListOf("yourobject"))
or
val myList = mutableListOf<MutableList<yourobject>>()

First, declare the master array which will contains other arrays
val masterList = mutableListOf<List<String>>()
Secondly, declare the arrays which will be nested. Assuming userID1, userID2, userID3, userID4 are declared somewhere
val subList1 = listOf(userID1,userID2)
val subList2 = listOf(userID3,userID4)
Finally, add the sublists to the master
masterList.add(subList1)
masterList.add(subList2)
Of course you can do all of this with only one line during masterList instantiation
val masterList = mutableListOf<List<String>>(
listOf(userID1,userID2),
listOf(userID3,userID4)
)

Change item's data type in a List or array in Kotlin

how can i change item's data type in arrays or lists in kotlin ?
i found a usual way but i need an easier and faster and better way to change data type of an array :)
fun typeChanger (data:MutableList<Number>): DoubleArray {
val result = mutableListOf<Double>()
for (i in data.iterator()){
result.add(i.toDouble())
}
return result.toDoubleArray()
}
val x = mutableListOf<Number>(+1,+1,-1,-1)
val xx:DoubleArray = typeChanger(x) // It works but i need an easier and faster and better way :)

Array map is your friend. You could keep your function and simplify, or remove it completely as below:-
val xx = x.map { it.toDouble() }
Once it's a list of doubles, you can then leave as a list or use .toDoubleArray() if you need an array.

What is the difference between map and mapTo in Kotlin

Trying to understand the difference between map and mapTo in kotlin. Could anyone help me out in explaining the difference using some examples

map creates a new list internally, and puts its results into that list, then it returns that list:
val mapResult = listOf(1, 2, 3).map { it * 2 } // you get a new list instance returned
If you use mapTo instead, you can specify the destination where it places the mapped elements, by providing your own list as the first parameter:
val myList = ArrayList<Int>()
val mapToResult = listOf(1, 2, 3).mapTo(myList) { it * 2 }
If the list you're provided already has elements in it, those will be kept, and the new ones will be added to those. It also returns the destination list for convenience.

map: map can transform your data(List) and can return either complete modified list or List of a variable of model, for ex:
You have a model:
data class Student(var id:String, var name:String, var className:String)
Now from arrayOfStudent, we want all the name of students in capital letters, so apply map like this:
val listOfNamesInCapitalLetters= arrStudent.map {
it.name= it.name.toUpperCase()
}
Log.d("map_test", "student's name: $listOfNamesInCapitalLetters")
The output will be:
[AMIT, VIJAY, SUMIT, KARAN, SMAEER]
Now, what if you want the whole student list, with name in capital letters and className is increased by 1, let's do this:
val result= arrStudent.map {
it.name= it.name.toUpperCase() // transforming name to upper case
it.className=it.className+1 // increasing class by 1
it // <- Note that we return it, because list will be prepared of the object which is returned by last statement of map
}
Log.d("modified_list", result.toString())
The output will be:
[Student(id=1, name=AMIT, className=6), Student(id=2, name=VIJAY, className=7), Student(id=3, name=KARAN, className=8), Student(id=4, name=VIRAT, className=9), Student(id=5, name=SAM, className=10)]
mapTo: If you want to transform your list into a different type of list then use mapTo, for example, we have a different data class named: CompactStudent
data class CompactStudent(val id:String, val name:String)
Now if we want to convert List to List, note that CompactStudent contains id and name but not the className as compared to Student model, so to do this:
val arrayList=ArrayList<CompactStudent>()
arrStudent.mapTo(arrayList){
CompactStudent(it.id,it.name)
}
Log.d("studentCompact", arrayList.toString())
Output will be:
[StudentCompct(id=1, name=AMIT), StudentCompct(id=2, name=VIJAY), StudentCompct(id=3, name=KARAN), StudentCompct(id=4, name=VIRAT), StudentCompct(id=5, name=SAM)]

How to retrieve data from ArrayList<ModelObject> not from ArrayList<String>?

Hi I'm still new to java data management.
I have a model object class named Computer which has 3 fields: processor, ram, hddSize.
I created a ArrayList
ArrayList<Computer> myCompList = new ArrayList<Computer>();
Computer comp1 = new Computer();
comp1.setProcessor("1.5 GHZ");
comp1.setRam("512 MB");
comp1.setHddSize("100 GB");
Computer comp2 = new Computer();
comp2.setProcessor("2.5 GHZ");
comp2.setRam("512 MB");
comp2.setHddSize("50 GB");
myCompList.add(comp1);
myCompList.add(comp2);
Now How can I retrieve data at index1 of the ArrayList above?
PS: I know how to do it if its a ArrayList< String> by convert it to String[] and then String[index].

Look at the Javadocs for ArrayList
This is where you should check for simple questions like this. The answer can be found in the "Method Summary" section.

Assuming that you have created getters and setters in your Computer class:
String processor = myCompList.get(1).getProcessor();
String ram = myCompList.get(1).getRam();
String hddSize = myCompList.get(1).getHddSize();

Can't you just go myCompList.get(0); ?
An arraylist of objects is essentially the same as an arraylist of strings. The .get() method returns the specific object at the given index. Here is the documentation for ArrayList.

myCompList.get(index) will return you data on the given index, make sure index number wouldn't be greater than array size, it will give you index out of bounds exception.