I have the following set:
class Element (var Name:String, var Description: String)
var MoreElement: Set[Element] = Set(E1, E2, E3, ...)
How do I delete an Element in a set MoreElement by name.
I found this solution:
MoreElement -= (MoreElement find (_.Name == "nameOfElementToRemove")).get
but I would not use the get, because if you does not find the item is thrown an exception, however I do not want no exception.
MoreElement = MoreElement filterNot (_.Name == "nameOfElementToRemove")
The direct answer to you question is to use filter, meaning something like:
moreElements = moreElements.filter( _.name != "nameOfElementToRemove")
Note this will scan the set. If you want a set indexed by name, you should really use a Map.
However, some caveats:
A set is a collection of unique elements. In order to compare elements in the set, it uses the contained type's equality operator. In your case, the Element class needs to define the 'equals' method (and hashCode) so the set can effectively compare instances.
In addition, you need to keep in mind that Set is an immutable class in Scala, so in your example you're really creating a new set, despite using an operator that appears to modify the existing set.
If you want a mutable set, you need to import scala.collection.mutable.Set.
Related
With arrays you can use a subscript to access Array Elements directly. You can read or write to them. With Sets I am not sure of a way to write its Elements.
For example, if I access a set element matching a condition I'm only able to read the element. It is passed by copy and I can't therefore write to the original.
For example:
columns.first(
where: {
$0.header.last == Character(String(i))
}
)?.cells.append(value: addValue)
// ERROR: Cannot use mutating member on immutable value: function call returns immutable value
You can't just change things inside a set, because of how a (hash) set works. Changing them would possibly change their hash value, making the set into an invalid state.
Therefore, you would have to take the thing you want to change out of the set, change it, then put it back.
if var thing = columns.first(
where: {
$0.header.last == Character(String(i))
}) {
columns.remove(thing)
thing.cells.append(value: addValue)
columns.insert(thing)
}
If the == operator on Column doesn't care about cells (i.e. adding cells to a column doesn't suddenly make two originally equal columns unequal and vice versa), then you could use update instead:
if var thing = columns.first(
where: {
$0.header.last == Character(String(i))
}) {
thing.cells.append(value: addValue)
columns.update(thing)
}
As you can see, it's quite a lot of work, so maybe sets aren't a suitable data structure to use in this situation. Have you considered using an array instead? :)
private var _columns: [Column]
public var columns : [Column] {
get { _columns }
set { _columns = Array(Set(newValue)) }
// or any other way to remove duplicate as described here: https://stackoverflow.com/questions/25738817/removing-duplicate-elements-from-an-array-in-swift
}
You are getting the error because columns might be a set of struct. So columns.first will give you an immutable value. If you were to use a class, you will get a mutable result from columns.first and your code will work as expected.
Otherwise, you will have to do as explained by #Sweeper in his answer.
I want to select all elements that do not have the class "myclass". How can I do that in Cytoscape.js?
According to http://js.cytoscape.org/#selectors/data, "[^name] Matches elements if the specified data attribute is not defined", however a class is not a data attribute and ^.myclass does not work, neither does :not(.myclass).
The error is The selector :not(.myclass) is invalid.
Is there a way to negate classes?
If you want to get the negative class selector, you can do this:
cy.elements().not(cy.$('.yourClass'));
// in more detail
var allElements = cy.elements(); // get all elements
var negators = cy.$('.yourClass'); // get all elements with the class to negate
var result = allElements.not(negators); // gets the difference between the two collections
If you really want to achieve this by using selectors only, then you might add a data field to each element which has myclass (this can be done while adding the class), and then use [^myclass]
I have an array of words, some may or may not have typos.
potentialWords = ["hello", "lkasjdf", "hunry"]
What I want to do is, return an array of all valid words, and also those words that were able to be autocorrected using a function I created correctWord. It returns an array of potential matches. so "hunry" might return ["hungry", "hurry"]. I will select the first index for the best guess.
Some words cannot be corrected however! e.g. "lkasjdf" will not find any corrections, but "hunry" will.
I was trying something like:
potentialWords.map {
if correctWord($0) != nil {
return correctWord($0)[0]
}
}
of course this will complain and say that I need a return outside the if clause. I can filter the list based on if the word can be corrected, and then map over the filtered list, re-checking which words need to be corrected, but this runs the correctWord function way too many times, and it is very sensitive.
I would like to be able to do one single pass through, and return an array of all valid words, and also corrected words.
P.S. I am calling correctWord twice in the map function for brevity, but of course I would assign correctWord($0) to a variable, and then if it isn't nil, take the first index and add it to the new list.
I think you're after flatMap. It's the same as map except it will also filter out any nil values.
potentialWords.flatMap { correctWord($0)?.first }
I'm fairly new to lua and have the following problem with an assignment from a class:
We currently extend lua to support objects and inheritance. The Syntax for that is
Class{'MyClass',
attribute1 = String,
attribute2 = Number
}
Class{'MySubClass', MyClass,
attribute3 = Number
}
This works perfectly fine. The real problem lies within the next task: We should support "recursive types", that means a call like
Class{'MyClass', attribute = MyClass}
should result in an class with a field of the same type as the class. When this "class-constructor" is called the variable MyClass is nil, thats why the parameter table doesnt't have an entry attribute. How is it possible to access this attribute?
My first thought was using some kind of nil-table which gets returned every time the global __index is called with an unset key. This nil-table should behave like the normal nil, but can be checked for in the "class-constructor". The problem with this approach are comparisons like nil == unknown. This should return true, but as the __eq meta method of the nil-table is never called we cannot return true.
Is there another approach I'm currently just ignoring? Any hint is greatly appreciated.
Thanks in advance.
Edit:
Here the relevant part of the "testfile". The test by which the code is rated in class is another one and gets published later.
three = 3
print( three == 3 , "Should be true")
print( unknown == nil , "Should be true" )
Class{'AClass', name = String, ref = AClass}
function AClass:write()
print("AClass:write(), name of AClass:", self.name)
end
aclass = AClass:create("A. Class")
aclass:write()
Since MyClass is just a lookup in the global table (_G), you could mess with its metatable's __index to return a newly-defined MyClass object (which you would later need to fill with the details).
However, while feasible, such an implementation is
wildly unsafe, as you could end up with an undefined class (or worse, you may end up inadvertantly creating an infinite lookup loop. Trust me, I've been there)
very hard to debug, as every _G lookup for a non-existing variable will now return a newly created class object instead of nil (this problem could somewhat be reduced by requiring that class names start with an uppercase character)
If you go that route, be sure to also override __newindex.
How about providing the argument in string form?
Class{'MyClass', attribute = 'MyClass'}
Detect strings inside the implementation of Class and process them with _G[string] after creating the class
Or alternatively, use a function to delay the lookup:
Class{'MyClass', attribute = function() return MyClass end}
Is there a way of creating method for setting the value in the Model's fields without setting the values explicitly like -
ModelName.create.fieldName1("value").fieldName2("value2") and so on
Can we iterate through all available fields of that model and set their values form some list-of-values ?
something like ...
Model.allFields.foreach((fld)=> {
fld.set(valueList(indx)); indx+=1
}
Actually I want to set values into all models using some generic method that works for all models.
According to my comment:
val list = List(...)
val record = YourRecordClass.createRecord
record.allFields.zip(list).foreach {case(field,value) => field.setFromAny(value)}