Kotlin has some pretty cool functions for collections. However, I have come across a problem in which the solution is not apparent to me.
I have a List of Objects. Those Objects have an ID field which coincides with a SQLite database. SQL operations are performed on the database, and a new list is generated. How can the index of an item from the new list be found based on the "ID" field (or any other field for that matter)?
the Collection.find{} function return the object, but not the index.
indexOfFirst can find the index of the first element of a collection that satisfies a specified predicate.
We have a DB SQlite that a call is made to to retrieve parentList We can obtain the items in the ArrayList with this type of code
fun onDoIt(view: View){
initDB()
for (t in 0..X-1) {
var N:String = parentList[t].dept
// NOTE two syntax here [t] and get(t)
if(t == 1){
var B:String = parentList[0].idD.toString()
println("$$$$$$$$$$$$$$$$$$$$$ ====== "+B)
}
var I:String = parentList.get(t).idD.toString()
println("################### id "+I+" for "+N)
}
}
private fun initDB() {
parentList = db.querySPDept()
if (parentList.isEmpty()) {
title = "No Records in DB"
} else {
X = parentList.size
println("**************************************** SIZE " + X)
title = "SP View Activity"
}
}
Related
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
Good afternoon, I want to make a universal sort for all tables. The idea is that the method will receive the name of the column as input and, through reflection, I will receive a link to the field of the same name.
val id = "id"
var a = JobSeekerTable::class
a.memberProperties.forEach { e ->
if (e.name == id) {
transaction {
JobSeeker.all().sortedBy { e.getter }
}
}
}
Unfortunately, this does not work. There was an option, through the fields field that the table has
JobSeekerTable.fields.forEach {v->
transaction {
JobSeeker.all().sortedBy { v }
}
}
but also unsuccessfully :(
If there is any way to refer to the required field through the name. Not using if and stuff like that?
First, you are probably looking for orderBy, not sortedBy. The former is to order SQL query results, the later is to sort a collection.
Second, you want to pass an instance of a column:
val id = "id"
JobSeekerTable.selectAll().orderBy(JobSeekerTable.columns.find {
it.name == id // Here I used the name you provided, although probably it should be named something like columnName
} !! to SortOrder.ASC)
Using "screaming" operator (!!) in Kotlin is a bad practice. So if all of your tables have ID column, for example, you can use "elvis" operator instead.
JobSeekerTable.selectAll().orderBy((JobSeekerTable.columns.find {
it.name == id
} ?: JobSeekerTable.id) to SortOrder.ASC)
I have an object media that holds descriptions which is a list. I'd love to see some elegant logic in Kotlin to add an element to that descriptions if the field is not null or add a fresh new list (with an initial element) to that field if it is null.
Pseudo:
if (media.descriptions == null) { media.descriptions = listOf("myValue")}
else { media.descriptions.add("myValue") }
I would probably do it the other way around, except you need to alter media itself (see below), i.e. creating your list first and add all the other entries to that list if media.descriptions isn't null:
val myDescriptions = mutableListOf("myValue") // and maybe others
media.descriptions?.forEach(myDescriptions::add)
If you need to manipulate descriptions of media, there is not so much you can do to make it more readable...:
if (media.descriptions == null) {
media.descriptions = mutableListOf("myValue") // just using mutable to make it clear
} else {
media.descriptions += "myValue"
}
or maybe:
if (media.descriptions == null) {
media.descriptions = mutableListOf<String>()
}
media.descriptions?.add("myValue")
You can use the elvis ?: operator to assign the list.
The simplest way I can think of is
media.descriptions = media.descriptions ?: listOf("myValue")
media.descriptions.add("myValue")
I am trying to perform a SELECT on the M1lhao table of Sorteio entity (database).
I don't want to go the traditional "string query" or AddWithParameter() way, i wanted to use the MVC4 EF5 available methods.
The following code passes the entire Table to the View, that i can do a foreach in the View and all works fine. What i am looking for is how can i do a SQL query, so i can pass only the element(s) i want, sorted DESCending (for example), obviously on a List and obeying the Model that the View expects.
Essentially i want a replacement for (i tried variants too, db.Milhao, etc):
var data = db.Database.ExecuteSqlCommand("SELECT * From M1lhao WHERE DrawID = {0}", id);
The problem with Find() is that it only searches primary keys.
The complete code:
public class M1lhaoController : Controller
{
private Sorteio db = new Sorteio();
public ActionResult Index(int id = 1)
{
var data = db.Database.ExecuteSqlCommand("SELECT * From M1lhao WHERE DrawID = {0}", id); // the variable data comes as -1
M1lhao m1lhao = db.M1lhao.Find(id);
if (m1lhao == null)
{
return HttpNotFound();
}
return View(db.M1lhao.ToList());
}
}
Thank you.
You can try as shown below.
var data = db.M1lhao.Where(m=>m.DrawID == id).Select(p=>p);
You can learn more about Method-Based Query Syntax : Projection
I have a list:
Dim list As New List(Of String)
with the following items:
290-7-11
1255-7-12
222-7-11
290-7-13
What's an easy and fast way to search if duplicate of "first block" plus "-" plus "second block" is already in the list. Example the item 290-7 appears twice, 290-7-11 and 290-7-13.
I am using .net 2.0
If you only want to know if there are duplicates but don't care what they are...
The easiest way (assuming exactly two dashes).
Boolean hasDuplicatePrefixes = list
.GroupBy(i => i.Substring(0, i.LastIndexOf('-')))
.Any(g => g.Count() > 1)
The fastest way (at least for large sets of strings).
HashSet<String> hashSet = new HashSet<String>();
Boolean hasDuplicatePrefixes = false;
foreach (String item in list)
{
String prefix = item.Substring(0, item.LastIndexOf('-'));
if (hashSet.Contains(prefix))
{
hasDuplicatePrefixes = true;
break;
}
else
{
hashSet.Add(prefix);
}
}
If there are cases with more than two dashes, use the following. This will still fail with a single dash.
String prefix = item.Substring(0, item.IndexOf('-', item.IndexOf('-') + 1));
In .NET 2.0 use Dictionary<TKey, TValue> instead of HashSet<T>.
Dictionary<String, Boolean> dictionary= new Dictionary<String, Boolean>();
Boolean hasDuplicatePrefixes = false;
foreach (String item in list)
{
String prefix = item.Substring(0, item.LastIndexOf('-'));
if (dictionary.ContainsKey(prefix))
{
hasDuplicatePrefixes = true;
break;
}
else
{
dictionary.Add(prefix, true);
}
}
If you don't care about readability and speed, use an array instead of a list, and you are a real fan of regular expressions, you can do the following, too.
Boolean hasDuplicatePrefixes = Regex.IsMatch(
String.Join("#", list), #".*(?:^|#)([0-9]+-[0-9]+-).*#\1");
Do you want to stop user from adding it?
If so, a HashTable with the key as first block-second block could be of use.
If not, LINQ is the way to go.
But, it will have to traverse the list to check.
How big can this list be?
EDIT: I don't know if HashTable has generic version.
You could also use SortedDictionary which can take generic arguments.
If you're list contains only strings, then you can simply make a method that takes the string you want to find along with the list:
Boolean isStringDuplicated(String find, List<String> list)
{
if (list == null)
throw new System.ArgumentNullException("Given list is null.");
int count = 0;
foreach (String s in list)
{
if (s.Contains(find))
count += 1;
if (count == 2)
return true;
}
return false;
}
If you're numbers have a special significance in your program, don't be afraid to use a class to represent them instead of sticking with strings. Then you would have a place to write all the custom functionality you want for said numbers.