I have list of three set of values which are related to each other. i.e. Roll Number, Student Name and School Name.
I am using Kotlin Triple to store them.
Below is the code:
val studentData = listOf(
Triple(first = "1", second ="Sam", third = "MIT"),
Triple(first = "2", second ="Johnny", third = "SYM"),
Triple(first = "3", second ="Depp", third = "PIT")
)
And now I need to build a function which will accept roll number and will return either student name or school name. Something like below:
fun getStudentDetails(rollNumber: String) : String {
//...
//return student name or school name
}
How to achieve this?
How to traverse the Triple in most preformat way considering below:
a) the time and space complexity
b) the list of student details can grow large
Given that rollNumber is a String you can just filter the list using firstOrNull and return the student name or school name:
fun getStudentDetails(rollNumber: String) : String =
studentData.firstOrNull({ (roll, _, _) ->
roll == rollNumber
})?.second ?: "No student with $rollNumber"
The space complexity would be constant, the time complexity is O(n) at the worst case.
Related
Is there an easier approach to convert an Intellij IDEA environment variable into a list of Tuples?
My environment variable for Intellij is
GROCERY_LIST=[("egg", "dairy"),("chicken", "meat"),("apple", "fruit")]
The environment variable gets accessed into Kotlin file as String.
val g_list = System.getenv("GROCERY_LIST")
Ideally I'd like to iterate over g_list, first element being ("egg", "dairy") and so on.
And then ("egg", "dairy") is a tuple/pair
I have tried to split g_list by comma that's NOT inside quotes i.e
val splitted_list = g_list.split(",(?=(?:[^\\\"]*\\\"[^\\\"]*\\\")*[^\\\"]*\$)".toRegex()).toTypedArray()
this gives me first element as [("egg", second element as "dairy")] and so on.
Also created a data class and tried to map the string into data class using jacksonObjectMapper following this link:
val mapper = jacksonObjectMapper()
val g_list = System.getenv("GROCERY_LIST")
val myList: List<Shopping> = mapper.readValue(g_list)
data class Shopping(val a: String, val b: String)
You can create a regular expression to match all strings in your environmental variable.
Regex::findAll()
Then loop through the strings while creating a list of Shopping objects.
// Raw data set.
val groceryList: String = "[(\"egg\", \"dairy\"),(\"chicken\", \"meat\"),(\"apple\", \"fruit\")]"
// Build regular expression.
val regex = Regex("\"([\\s\\S]+?)\"")
val matchResult = regex.findAll(groceryList)
val iterator = matchResult.iterator()
// Create a List of `Shopping` objects.
var first: String = "";
var second: String = "";
val shoppingList = mutableListOf<Shopping>()
var i = 0;
while (iterator.hasNext()) {
val value = iterator.next().value;
if (i % 2 == 0) {
first = value;
} else {
second = value;
shoppingList.add(Shopping(first, second))
first = ""
second = ""
}
i++
}
// Print Shopping List.
for (s in shoppingList) {
println(s)
}
// Output.
/*
Shopping(a="egg", b="dairy")
Shopping(a="chicken", b="meat")
Shopping(a="apple", b="fruit")
*/
data class Shopping(val a: String, val b: String)
Never a good idea to use regex to match parenthesis.
I would suggest a step-by-step approach:
You could first match the name and the value by
(\w+)=(.*)
There you get the name in group 1 and the value in group 2 without caring about any subsequent = characters that might appear in the value.
If you then want to split the value, I would get rid of start and end parenthesis first by matching by
(?<=\[\().*(?=\)\])
(or simply cut off the first and last two characters of the string, if it is always given it starts with [( and ends in )])
Then get the single list entries from splitting by
\),\(
(take care that the split operation also takes a regex, so you have to escape it)
And for each list entry you could split that simply by
,\s*
or, if you want the quote character to be removed, use a match with
\"(.*)\",\s*\"(.*)\"
where group 1 contains the key (left of equals sign) and group 2 the value (right of equals sign)
I have a class called Person
data class Person(
val id: Int,
val name: String
)
data class IDs(
val id : Int,
val active : Boolean )
and an array list that has numbers of ids and another list of Persons
val myStu = listOf<Person>(Person(1, "Name_1"), Person(2, "Name_2"), Person(3, "Name_3"))
var ids = listOf<IDs>(IDs(1,false),IDs(2,true),IDs(3,true))
var newIds = listOf<Int>(2,3,4,6)
First I want to apply two actions to the myStu, first is to have a list that include all the items from myStu that his id matches the id in the IDS and only if the active is true
myStu or the new list will have the values
Person(2, "Name_2"), Person(3, "Name_3"))
Then do action two , I need to add a new item to the new list that their id does not exist in the newIds , in another word we will add a new person Person(4,"None") and (6,"None) , 4 and 6 values come from newIds list
the final output will be :
id= 2 name = "Name_2", id= 3 name = "Name_3", id= 4 name = "None" , id =6 name="None"
I want to write the code with filter , I failed with first step because I don't know how to use contains() with the list inside the filter
val newArr = myStu.filter {
ids.contains(it.id)
}
The "easiest" way of doing that would be to use filter directly, there's no need for contains. If we were to use contains, then we would need to also search for which element contained the id, in order to get the status. We can just do a .any() to do both at the same time.
V1
val activeStu = myStu.filter { person -> ids.any { it.id == person.id && it.active } }
val result = newIds.map { newId ->
activeStu.find { it.id == newId } ?: Person(id = newId, name = "None")
}
Another method, that might work a bit better if we have big lists, would be to first transform the IDs list into a map. That way the second part of our code is a bit more efficient, since there is no search involved.
V2
val idsMap = ids.associate { it.id to it.active }
val activeStu = myStu.filter { idsMap[it.id] ?: false }
//the creation of the result list is the same
Version without creating 2 new lists. This works, but it might be quite ineficient processing wise, and also harder to understand what is going on IMO.
V3
val result = newIds.map { newId ->
//try to find an IDs with the current newId and status as true
when (ids.find { it.id == newId }?.active) {
//if found, then find the corresponding Person
true -> myStu.find { it.id == newId } ?: Person(newId, "None") // if this happens, it means that an IDs with status true existed and no Person had that id. Not sure what you want in this scenario, this version creates one of the "none" persons.
//if not found, then create a new one
else -> Person(newId, "None")
}
}
Note: depending on what version of kotlin you have, you might have to change the when statement to this:
when (ids.find { it.id == newId }?.active == true)
Since I think I remember that null didn't used to be treated as false in old versions (I've run this with version 1.4.20).
Btw, you can also use this version with the idsMap from V2, just replace the when(...) with when(idsMap[newId] or when(idsMap[newId] == true) depending on the kotlin version.
There is a data class as fruits.
data class Fruits(
val code: String, //Unique
val name: String
)
The base list indexed items with boolean variable is as below.
val indexList: MutableList<Boolean> = MutableList(baseFruitList.size) { false }
Now the Favourite Indexed list is as below
val favList: MutableList<Boolean> = MutableList(favFruitList.size) { true}
I want a combined full list which basically has the fav item indicated as true.
Ex:
baseFruitList = {[FT1,apple],[FT2,grapes],[FT3,banana],[FT4,mango],[FT5,pears]}
favList = {[FT2,grapes],[FT4,mango]}
The final index list should have
finalIndexed = {false,true,false,true,false}
How can we achieve in Kotlin, without iterating through each element.
You can do
val finalIndexed = baseFruitList.map { it in favList }
assuming, like #Tenfour04 is asking, that name is guaranteed to be a specific value (including matching case) for a specific code (since that combination is how a data class matches another, e.g. for checking if it's in another list)
If you can't guarantee that, this is safer:
val finalIndexed = baseFruitList.map { fruit ->
favList.any { fav.code == fruit.code }
}
but here you have to iterate over all the favs (at least until you find a match) looking to see if one has the code.
But really, if code is the unique identifier here, why not just store those in your favList?
favList = listOf("FT2", "FT4") // or a Set would be more efficient, and more correct!
val finalIndexed = baseFruitList.map { it.code in favList }
I don't know what you mean about "without iterating through each element" - if you mean without an explicit indexed for loop, then you can use these simple functions like I have here. But there's always some amount of iteration involved. Sets are always an option to help you minimise that
I am working with some datasets in my room database, and my method is to have one table with information about a dataset called DatasetInfo which stores things like name, type of value stored, id, etc; and a second table where I store the values in 3 columns: (id, date, value). This ordered triplet is defined as a DatasetValue entity. Here, (date, value) is an ordered pair that I want to plot.
To plot these ordered pairs, I have to convert them to a list of Entry objects, where Entry takes the values x and y. It makes the most sense to query my database and simply ask for List<Entry>, because right now I ask for List<DatasetValue> and then I have to map that result to List<Entry> which is unnecessary.
I query for the dataset information table DatasetInfo as follows:
data class DatasetWithValues(
#Embedded
var datasetInfo: DatasetInfo,
#Relation(
parentColumn = DATASET_COLUMN_DATASET_ID,
entityColumn = VALUES_COLUMN_ID,
entity = DatasetValue::class,
)
var values : List<Entry>
)
Now, as I said above, Entry has values x and y, and Dataset calls them date and value. Of course, when I ask for this relation, it will fail because it doesn't know how to assign values from a table with the columns id, date, and value to an object which takes x and y. So, I define a new class:
class DatasetEntry(
#ColumnInfo(name = "date")
var date : Float,
#ColumnInfo(name = "value")
val value : Float
) : Entry(date, value)
and then make the following adjustment:
//var values : List<Entry>
var values : List<DatasetEntry>
That does nothing. The code doesn't compile because:
SQL error or missing database (no such column: x)
Well, what if I instead write:
class DatasetEntry(
#ColumnInfo(name = "date")
var date : Float,
#ColumnInfo(name = "value")
val value : Float
) : Entry(){
init{
x = date
y = value
}
}
That doesn't help either, same error. Even if I remove that init call, it still wants x.
The plot thickens, because inside of Entry I can see x is declared private. So I have absolutely no clue what is happening here. How does Room even know to look for x? Is there any work around for this other than renaming the columns in my table to x and y?
Is there any work around for this other than renaming the columns in my table to x and y?
If you have such option it would be the easiest. Still there are some options you could consider:
1. Mapping Room's result to needed one
So, you ask Room for some raw result and then map it to ready one. For that you add 2 classes:
data class DatasetWithValuesRaw(
#Embedded
var datasetInfo: DatasetInfo,
#Relation(
parentColumn = DATASET_COLUMN_DATASET_ID,
entityColumn = VALUES_COLUMN_ID,
)
var values : List<DatasetValue>
)
data class DatasetWithValuesReady(
var datasetInfo: DatasetInfo,
var values : List<Entry>
)
Let's say you have a dao method:
Query("select * ....")
fun getRawData(): List<DatasetWithValuesRaw>
For mapping you use:
fun getReadyData() =
getRawData().map { item ->
DatasetWithValuesReady(item.datasetInfo,
item.values.map { Entry(x = it.date, y = it.value)
}) }
2. Replacing Room's #Relation with explicit query
It's not what you really want, but still is an option.
Use class like that:
data class DatasetWithSeparateValues(
#Embedded
var datasetInfo: DatasetInfo,
#Embedded
var value : Entry // <----- it's not a list, just a single value
)
and in your dao you set query with explicit columns' names (x and y). Something like that:
Query("SELECT *, values.date as x, values.value as y FROM dataset LEFT JOIN values on dataset.DATASET_COLUMN_DATASET_ID = values.VALUES_COLUMN_ID")
fun getData(): List<DatasetWithSeparateValues>
As a result you'll get a list, but if there is a one dataset with 5 values you'll get inside list 5 items with the same dataset and separate values. After that you could use Kotlin collection's methods (groupBy for example) to prettify result in some way
I'm consuming a client that I cannot change and it sends me data that looks like that:
"BOOKING - PAID (price.amount=70, price.currency=EUR)"
and I would like to retrieve from that only 70 EUR
What is the best way to do such thing in kotlin? I didn't find any removeAll("", "", ...) functions for String, only replace but would have to chain them to remove both price.amount and price.currency.
EDIT:
Need to get BOOKING - PAID (70 EUR) actually, forgot about that part.
Thinking about it and as you updated your question to really remove only a part from the string, here are some approaches for removing several strings from a given string:
Using regex:
input.replace("""(price\.(amount|currency)=|,)""".toRegex(), "")
Using a list of strings to remove:
sequenceOf(input, "price.amount=", ",", "price.currency=")
.reduce { acc, rm -> acc.replace(rm, "") }
// alternatively using var:
var input = TODO()
sequenceOf("price.amount=", ",", "price.currency=")
.forEach { input = input.replace(it, "") }
Still: most of the time I would rather take the other route: extracting the information you require and just print that, as also Baptiste has shown in his answer. Otherwise you may start to expose answers of that service you didn't want to expose in the first place.
This sounds like a job for regular expressions!
fun main(args: Array<String>) {
val str = "BOOKING - PAID (price.amount=70, price.currency=EUR)"
// The expressions between parentheses will map to groups[1], groups[2] and groups[3] respectively
val reg = Regex("""(.*) \(price\.amount=([0-9]+), price\.currency=([A-Z]+)\)""")
// Apply the regular expression on the string
val results = reg.find(str)
results?.groupValues?.let { groups ->
// If results and groupValues aren't null, we've got our values!
val type = groups[1]
val price = groups[2]
val currency = groups[3]
println("$type ($price $currency)") // BOOKING - PAID (70 EUR)
}
// Or as suggested by #Roland:
results?.destructured?.let { (type, price, currency) ->
println("$type ($price $currency)") // BOOKING - PAID (70 EUR)
}
}
Regular expressions allow you to take a string as entry, and find a pattern in it. They're quite used in all languages, you can find more info about them all over the place.
EDIT: edited for the updated question. I chose to treat "BOOKING - PAID" as a single string, but there's an infinite number of ways to do it, depending on your granularity needs; and honestly, at that point a regex might be a bit overkill. :)
Without regex by string manipulation and assuming that this is the pattern:
fun main(args: Array <String> ) {
val str = "BOOKING - PAID (price.amount=70, price.currency=EUR)"
val type = str.substringBefore("(").trim()
val price = str.substringBeforeLast(",").substringAfter("=")
val currency = str.substringAfterLast("=").substringBefore(")")
val result = "$type ($price $currency)"
println(result)
}
will print
BOOKING - PAID (70 EUR)
Edit: I use str.substringBeforeLast(",") to get the price, in case , could be used as a delimeter for decimal part in the number