I want to reorder the string "hearty" to be in alphabetical order: "aehrty"
I've tried:
val str = "hearty"
val arr = str.toCharArray()
println(arr.sort())
This throws an error. I've also tried the .split("") method with the .sort(). That also throws an error.
You need to use sorted() and after that joinToString, to turn the array back into a String:
val str = "hearty"
val arr = str.toCharArray()
println(arr.sorted().joinToString("")) // aehrty
Note: sort() will mutate the array it is invoked on, sorted() will return a new sorted array leaving the original untouched.
So your issue is that CharArray.sort() returns Unit (as it does an in-place sort of the array). Instead, you can use sorted() which returns a List<Char>, or you could do something like:
str.toCharArray().apply { sort() }
Or if you just want the string back:
fun String.alphabetized() = String(toCharArray().apply { sort() })
Then you can do:
println("hearty".alphabetized())
Related
#file:Suppress("UNCHECKED_CAST")
data class Element<T>(
val key: String,
val valueOne: T,
val valueTwo: T,
val comparator: Comparator<T>,
val comparatorValue: CompareResult
)
enum class CompareResult(
val value: Int
) {
LESS(-1),
EQUAL(0),
GREATER_THAN(1)
}
fun <T> matchesComparison(list:Collection<Element<T>>): Pair<Boolean, List<String>> {
val failedComparisons = mutableListOf<String>()
for (element in list) {
val compareValue = element.comparator.compare(element.valueOne, element.valueTwo)
if (element.comparatorValue.value != compareValue) {
failedComparisons.add(element.key)
}
}
return Pair(failedComparisons.isEmpty(), failedComparisons)
}
val stringComparator = Comparator.comparing(String::toString)
val intComparator = Comparator.comparing(Int::toInt)
val elementsToCompare = listOf(
Element("number", 1, 2, intComparator, CompareResult.LESS),
Element("first name", "a", "a", stringComparator, CompareResult.EQUAL),
Element("last name", "a", "b", stringComparator, CompareResult.EQUAL)
)
matchesComparison(elementsToCompare).second.joinToString(", ","Failed elements: \"","\"")
I often get faced with comparing two different object properties with the same values.
As an example object A has props number,firstname,lastname. What i want to do is create a list have and have a function which goes over these Elements and returns which props have failed the comparison. I've managed to use generics for both the object and the matchesComparison function which returns the failed comparisons. The problem begins when i want to pass this list which is of type Collection<Element<out Any>> to this function is i get a type missmatch. instead of using unchecked casts to force the Comparator to be of type Any i would like to do this
val stringComparator = Comparator.comparing(String::toString)
val intComparator = Comparator.comparing(Int::toInt)
The result value that of the script above should be Failed elements: "last name"
I tried changing the signature of the function to out any but then the comparator.compare method has both params as of type Nothing. I really want to avoid unsing unchecked casts.
matchesComparison() doesn't need to be generic in this case. It doesn't really care what is the type of the whole input collection, so we can simply use * here.
Then we have another problem. The compiler isn't smart enough to notice that while we perform operations on a single element, all its properties are of matching types. As a result, it doesn't allow to use element.comparator on element.valueOne and element.valueTwo. To fix this problem, we simply need to create a separate function which works on a single Element, so it understand the type for all properties is the same:
fun matchesComparison(list:Collection<Element<*>>): Pair<Boolean, List<String>> {
fun <T> Element<T>.matches() = comparatorValue.value == comparator.compare(valueOne, valueTwo)
val failedComparisons = mutableListOf<String>()
for (element in list) {
if (!element.matches()) {
failedComparisons.add(element.key)
}
}
return Pair(failedComparisons.isEmpty(), failedComparisons)
}
Also, I believe such matches() function should be actually a member function of Element. It seems strange that while Element is pretty independent and it contains everything that is needed to perform a comparison, it still requires to use external code for this. If it would have a matches() function then we wouldn't need to care about its T. matches() would work with any Element.
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)
Causing the data to be sorted from back to front
fun main() {
val fruits = listOf("apple", "banana", "kiwifruit")
var index = 0
while(fruits.size > index){
println("${fruits[index]}")
index++
}
}
I cannot comment (low-rep).
use mutable list (sorting is usually modifies the collection)
iterate via the language provided methods
https://pl.kotl.in/SC-8aXFJJ
In Kotlin, how can I take the first n elements of this array:
val allColours = arrayOf(
Pair(Color.RED, Color.WHITE),
Pair(Color.RED, Color.BLACK),
Pair(Color.YELLOW, Color.BLACK),
Pair(Color.GREEN, Color.WHITE),
Pair(Color.BLUE, Color.WHITE),
Pair(Color.BLUE, Color.WHITE),
Pair(Color.CYAN, Color.BLACK),
Pair(Color.WHITE, Color.BLACK))
So how can I fill pegColours with the first say 3 Pairs?
var pegColours: Array<Pair<Color,Color>> = //???
I tried allColours.take but it gave an error:
Expecting an element
You need to specify the number of items you want to take.
allColours.take(3)
For a random number of random indices, you can use the following:
val indexes = arrayOf(2, 4, 6)
allColours.filterIndexed { index, s -> indexes.contains(index) }
Note that you can write an extension method for this:
fun <T> Array<T>.filterByIndices(vararg indices: Int) = filterIndexed { index, _ -> indices.contains(index) }
Alternatively, if the indices are consecutive, you can use slice:
allColours.slice(1..3)
The problem with your code that you create pairs with color constants which are Ints (allColours has type Array<Pair<Int, Int>>), but you expect Array<Pair<Color, Color>>. What you have to do is change type pegColours type and use take:
var pegColours: Array<Pair<Int, Int>> = allColours.take(3).toTypedArray()
Also you have to call toTypedArray() cause Array.take returns List rather than Array. Or you can change pegColours type as following:
var pegColours: List<Pair<Int, Int>> = allColours.take(3)
I know you already proposed the usage of take, but alternatively ranges and a simple map also help to write idiomatic code as shown next:
var pegColours = (0 until 3)
.map { allColours[it] }
.toTypedArray()
You are very close :)
val allColours = arrayOf("red", "blue", "green")
kotlin.io.println(allColours.take(2))
Will give you first two elements ["red", "blue"]
You have to specify the number of elements you want to take from the array
I would like to swap a string from "abcde" to "bcdea". So I wrote my code as below in Kotlin
var prevResult = "abcde"
var tmp = prevResult[0]
for (i in 0..prevResult.length - 2) {
prevResult[i] = prevResult[i+1] // Error on preveResult[i]
}
prevResult[prevResult.length-1] = tmp // Error on preveResult[prevResult.lengt-1]
It errors out as stated above comment line. What did I do wrong? How could I fix this and get what I want?
Strings in Kotlin just like in Java are immutable, so there is no string.set(index, value) (which is what string[index] = value is equivalent to).
To build a string from pieces you could use a StringBuilder, construct a CharSequence and use joinToString, operate on a plain array (char[]) or do result = result + nextCharacter (creates a new String each time -- this is the most expensive way).
Here's how you could do this with StringBuilder:
var prevResult = "abcde"
var tmp = prevResult[0]
var builder = StringBuilder()
for (i in 0..prevResult.length - 2) {
builder.append(prevResult[i+1])
}
builder.append(tmp) // Don't really need tmp, use prevResult[0] instead.
var result = builder.toString()
However, a much simpler way to achieve your goal ("bcdea" from "abcde") is to just "move" one character:
var result = prevResult.substring(1) + prevResult[0]
or using the Sequence methods:
var result = prevResult.drop(1) + prevResult.take(1)
You can use drop(1) and first() (or take(1)) to do it in one line:
val str = "abcde"
val r1 = str.drop(1) + str.first()
val r2 = str.drop(1) + str.take(1)
As to your code, Kotlin String is immutable and you cannot modify its characters. To achieve what you want, you can convert a String to CharArray, modify it and then make a new String of it:
val r1 = str.toCharArray().let {
for (i in 0..it.lastIndex - 1)
it[i] = it[i+1]
it[it.lastIndex] = str[0] // str is unchanged
String(it)
}
(let is used for conciseness to avoid creating more variables)
Also, you can write a more general version of this operation as an extension function for String:
fun String.rotate(n: Int) = drop(n % length) + take(n % length)
Usage:
val str = "abcde"
val r1 = str.rotate(1)
Simpler solution: Just use toMutableList() to create a MutableList of Char and then join it all together with joinToString.
Example:
Given a String input, we want to exchange characters at positions posA and posB:
val chars = input.toMutableList()
val temp = chars[posA]
chars[posA] = chars[posB]
chars[posB] = temp
return chars.joinToString(separator = "")
Since Strings are immutable, you will have to copy the source string into an array, make changes to the array, then create a new string from the modified array. Look into:
getChars() to copy the string chars into an array.
Perform your algorithm on that array, making changes to it as needed.
Convert the modified array back into a String with String(char[]).