I rather have this ugly way of building a string from a list as:
val input = listOf("[A,B]", "[C,D]")
val builder = StringBuilder()
builder.append("Serialized('IDs((")
for (pt in input) {
builder.append(pt[0] + " " + pt[1])
builder.append(", ")
}
builder.append("))')")
The problem is that it adds a comma after the last element and if I want to avoid that I need to add another if check in the loop for the last element.
I wonder if there is a more concise way of doing this in kotlin?
EDIT
End result should be something like:
Serialized('IDs((A B,C D))')
In Kotlin you can use joinToString for this kind of use case (it deals with inserting the separator only between elements).
It is very versatile because it allows to specify a transform function for each element (in addition to the more classic separator, prefix, postfix). This makes it equivalent to mapping all elements to strings and then joining them together, but in one single call.
If input really is a List<List<String>> like you mention in the title and you assume in your loop, you can use:
input.joinToString(
prefix = "Serialized('IDs((",
postfix = "))')",
separator = ", ",
) { (x, y) -> "$x $y" }
Note that the syntax with (x, y) is a destructuring syntax that automatically gets the first and second element of the lists inside your list (parentheses are important).
If your input is in fact a List<String> as in listOf("[A,B]", "[C,D]") that you wrote at the top of your code, you can instead use:
input.joinToString(
prefix = "Serialized('IDs((",
postfix = "))')",
separator = ", ",
) { it.removeSurrounding("[", "]").replace(",", " ") }
val input = listOf("[A,B]", "[C,D]")
val result =
"Serialized('IDs((" +
input.joinToString(",") { it.removeSurrounding("[", "]").replace(",", " ") } +
"))')"
println(result) // Output: Serialized('IDs((A B,C D))')
Kotlin provides an extension function [joinToString][1] (in Iterable) for this type of purpose.
input.joinToString(",", "Serialized('IDs((", "))')")
This will correctly add the separator.
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 declared 2 variables to read from console but on other case i want to read just one of them but i can't.
My code:
print("Enter two numbers in format: {source base} {target base} (To quit type /exit) ")
val (sourceBase, targetBase) = readLine()!!.split(" ")
`I can't type /exit because i've got IndexOutOfBoundsException.
Any tips?
Edit: Thank you all for respond, especially lukas.j, it's working now.
Add a second element, an empty string, if the splitted readLine() contains less than 2 elements:
val (sourceBase, targetBase) = readLine()!!.split(" ").let { if (it.size < 2) it + "" else it }
I am trying to find out the native way to concatenate prefix to string, but only in case, it was not.
This code checks the text variable and makes it start with "#".
val text = "123456"
val prefix = "#"
val textFormatted = (if (text.startsWith(prefix)) "" else prefix ) + text
I hope there are clean solutions somewhere in Kotlin
An alternative would be to use removePrefix:
val textFormatted = prefix + text.removePrefix(prefix)
Otherwise you could also keep the if but write it the following way to avoid extra parentheses and extra concatenation, and also make the code closer to the semantics:
val textFormatted = if (text.startsWith(prefix)) text else "$prefix$text"
But your solution works too.
You can use the string interpolation from the kotlin, example:
val text:String = "123456#123456"
val prefix:String = "#"
val interpolation:String = "#${text.removePrefix(prefix)}"
I have written a code that reads a text file. The text files contain placeholders which I would like to replace. The substitution does not work this way and the string is printed with the placeholders. Here is the code that I have written for this:
class TestSub(val sub: Sub) {
fun create() = template()
fun template() = Files.newBufferedReader(ClassPathResource(templateId.location).file.toPath()).readText()
}
data class Sub(val name: String, val age: Int)
Here is the main function that tries to print the final string:
fun main(args: Array<String>) {
val sub = Sub("Prashant", 32)
println(TestSub(sub).create())
}
However, when, instead of reading a file, I use a String, the following code works (Replacing fun template())
fun template() = "<h1>Hello ${sub.name}. Your age is ${sub.age}</h1>"
Is there a way to make string Substitution work when reading the content of a file?
Kotlin does not support String templates from files. I.e. code like "some variable: $variable" gets compiled to "some variable: " + variable. String templates are handled at compile time, which means it does not work with text loaded from files, or if you do something else to get the String escaped into a raw form. Either way, it would, as danielspaniol mentioned, be a security threat.
That leaves three options:
String.format(str)
MessageFormat.format(str)
Creating a custom engine
I don't know what your file contains, but if it's the String you used in the template function, change it to:
<h1>Hello {0}. Your age is {1,integer}</h1>
This is for MessageFormat, which is my personal preference. If you use String.format, use %s instead, and the other appropriate formats.
Now, use that in MessageFormat.format:
val result = MessageFormat.format(theString, name, age);
Note that if you use MessageFormat, you'll need to escape ' as ''. See this.
String substitution using ${...} is part of the string literals syntax and works roughly like this
val a = 1
val b = "abc ${a} def" // gets translated to something like val b = "abc " + a + " def"
So there is no way for this to work when you load from a text file. This would also be a huge security risk as it would allow for arbitrary code execution.
However I assume that Kotlin has something like a sprintf function where you can have placeholders like %s in your string and you can replace them with values
Take a look here. It looks like the easiest way is to use String.format
You are looking for something similar to Kotlin String templates for raw Strings, where placeholders like $var or ${var} are substituted by values, but this functionality needs to be available at runtime (for text read from files).
Methods like String.format(str) or MessageFormat.format(str) use other formats than the notation with the dollar prefix of Kotlin String templates. For "Kotlin-like" placeholder substitution you could use the function below (which I developed for similar reasons). It supports placeholders as $var or ${var} as well as dollar escaping by ${'$'}
/**
* Returns a String in which placeholders (e.g. $var or ${var}) are replaced by the specified values.
* This function can be used for resolving templates at RUNTIME (e.g. for templates read from files).
*
* Example:
* "\$var1\${var2}".resolve(mapOf("var1" to "VAL1", "var2" to "VAL2"))
* returns VAL1VAL2
*/
fun String.resolve(values: Map<String, String>): String {
val result = StringBuilder()
val matcherSimple = "\\$([a-zA-Z_][a-zA-Z_0-9]*)" // simple placeholder e.g. $var
val matcherWithBraces = "\\$\\{([a-zA-Z_][a-zA-Z_0-9]*)}" // placeholder within braces e.g. ${var}
// match a placeholder (like $var or ${var}) or ${'$'} (escaped dollar)
val allMatches = Regex("$matcherSimple|$matcherWithBraces|\\\$\\{'(\\\$)'}").findAll(this)
var position = 0
allMatches.forEach {
val range = it.range
val placeholder = this.substring(range)
val variableName = it.groups.filterNotNull()[1].value
val newText =
if ("\${'\$'}" == placeholder) "$"
else values[variableName] ?: throw IllegalArgumentException("Could not resolve placeholder $placeholder")
result.append(this.substring(position, range.start)).append(newText)
position = range.last + 1
}
result.append(this.substring(position))
return result.toString()
}
String templates only work for compile-time Sting literals, while what u read from a file is generated at runtime.
What u need is a template engine, which can render templates with variables or models at runtime.
For simple cases, String.format or MessageFormat.format in Java would work.
And for complex cases, check thymeleaf, velocity and so on.
I get an error when using forNonBlank in OpenRefine's Templating Export feature.
I have cells with multiple subjects that I want to capture in separate dcterms:subject xml elements. Example:
Geology--Alberta--Coal Valley. // Geology, Structural. // Geology, Stratigraphic--Cretaceous.
I am using OpenRefine's Templating Export option to export to XML, similarly to the process described here.
This expression works fine:
{{forEach(cells["dcterms:subject"].value.split(" // "), v, "<dcterms:subject>" + v + "</dcterms:subject>\n")}}
I get:
<dcterms:subject>Geology--Alberta--Coal Valley.</dcterms:subject>
<dcterms:subject>Geology, Structural.</dcterms:subject>
<dcterms:subject>Geology, Stratigraphic--Cretaceous.</dcterms:subject>
But when using forNonBlank as in:
{{forNonBlank(cells["dcterms:subject"].value.split(" // "), v, "<dcterms:subject>" + v + "</dcterms:subject>\n", "")}}
I get:
<dcterms:subject>[Ljava.lang.String;#16657412</dcterms:subject>
Is there something wrong with my coding, or is this a bug?
Thanks for your help.
forNonBlank isn't an iterative function, so the function:
forNonBlank(cells["dcterms:subject"].value.split(" // "), v, "" + v + "\n", "")
Evaluates the array created through the split as to whether it is blank or not (the whole array, not each item in the array) and finding that it is not blank assigns the array to variable 'v'.
Essentially 'forNonBlank' is doing something similar to combining 'if' and 'isNonBlank', not 'forEach' and 'isNonBlank'
You've got several options for doing what you want, but you need to have an iterator in there somewhere. For example:
forEach(cells["dcterms:subject"].value.split(" // "),v,forNonBlank(v,w, "" + w + "", "")).join("/n")