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How to copy end of the Array in swift?
(6 answers)
Closed 6 years ago.
Swift's implementation of arrays is throwing me for a loop again! (Haw, haw.) All I want is to take an array of arbitrary length and get a new array (or an array slice) from it that has the first element removed.
Why is this so hard?
I just want to be able to do something like this:
let suffix = someArray.suffixFrom(1)
But I can't figure out how to do this. It seems the closest method I've found requires knowing the length of the array, which I don't know because it's computed inline and I really really hate having to split such a simple concept up into a bunch of variables and lines.
Elaboration:
I have a string split by colons (:) and I just want to create a Set containing all the :-delimited components excluding the first one.
So that a string "one:two:three" would return a set containing ["two", "three"]. Since I can create a Set from an array, all I really need is to get the suffix of the array, but I don't know how many components there are because it's inline:
return Set(attributeName?.componentsSeparatedByString(":").suffixFrom(1))
Why does Swift make this so hard?
Edit: Before a bunch of you suggest it, I'm well aware I could extend the array class to do this myself, but I'm writing a framework and I don't want to do that, and I also don't want to have to write a bloody utility function to do something so darned simple.
The CollectionType.dropFirst(_:) does exactly what you need, with the exact syntax you're looking for.
let suffix = someArray.dropFirst(1)
Related
First question on stackoverflow :)
I'm going through the Ruby course on Codecademy and I'm stuck on something.
fruits = ["orange", "apple", "banana", "pear", "grapes"]
fruits.sort! {|first, second| second <=> first}
print fruits
I don't know how to phrase this question. On Codecademy the assignment was to set up the array to be displayed in reverse on the console. After some research, I was able to figure it out. I understand how it works and the order to put it in the code not why. I'm aware that "<=>" compares two objects, but how do the items within the array become objects when we don't declare them as such?
Secondly, what is the purpose of writing this code in this way when we could do fruits.sort.reverse?
First question: At various points in its operation the sort method has to compare pairs of objects to see what their relative ordering should be. It does the comparison by applying the block you pass to sort, i.e., {|first, second| second <=> first}. Not sure what you mean by "how do the items within the array become objects when we don't declare them as such?". All data in ruby is an object, so there's no declaration or conversion needed given that all variables are object references.
Second question: Yes, you could do fruits.sort.reverse, but that would require additional work after the sort to do the reverse operation. Also, reverse can't handle more complex sorting tasks, such as sorting people by multiple criteria such as gender & last name, or hair color, height, and weight. Writing your own comparator can handle quite complex orderings.
String literals can be used to create string objects in Ruby, there is no need to use the String class to create the object. The following two are equivalent:
"Hello, world!"
String.new("Hello, world!")
More information can be found here.
Secondly, what is the purpose of writing this code in this way when we could do fruits.sort.reverse?
Please contact Codecademy about this, but I suspect it's for learning more about how <=> works.
Possibly very stupid question I cannot seem to find an answer for (I am beginning with code)
I want to create a simple loop which appends myArray with three objects, which are members of a custom class MyClass. The objects have the following names: "object1", "object2", "object3".
When I write the following code, there is no issue:
myArray.append(object1)
But I want to write a loop to add all three. Again, very dumb, but I can't figure out how to insert the number in the name of the object as a variable. E.g., here was something I tried
let x = 3
for i in 1...x {
myArray.append(object[i])
}
This gives an error. The reason I want to do it using a loop, and not simply write in the three objects manually, is that I won't always loop three times. Sometimes I'll just want the first two objects, sometimes just the first.
I assume there's some easy way to do this, but when I search it tends to turn up more complex questions
If I have an array with elements linked to xassets with names like "card1", "card2", etc up to "card100" is there a quicker way to write these elements in the array format without having to write out all 100?
Also if this has been answered already please let me know or link to it. About 2 days into trying to teach myself to program.
Not exactly sure what you're asking but you may want to look at loops - Swift Loops. You can add items to an array in a for loop from 1 to 100.
Is this what you are looking for ?
let cards = Array(1...100).map({"card\($0)"})
The question is quite simple but I can't find the answer.
I'm using j2me.
I have an integer array of 9 elements.
After all the computations now I want to print it or show it in a form.
It is something like Integer.toString(); for use with an array?
I know I can use a loop but I want to know if it's a faster way.
Use a loop but don't use the String + operator. Use StringBuffer.append().
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
What's the best way to make a deep copy of a data structure in Perl?
In my code i do:
#data_new=#data;
and then I change #data.
The problem is that #data_new always changes as well.
It's like #data_new is just a reference to what's in #data.
How do i make a copy of an array which is not a reference but a new copy of all the values?
#data is a two dimensional array, by the way.
See perlfaq4's "How do I print out or copy a recursive data structure". That is, use the dclone method from Storable.
use Storable qw(dclone);
#data_new = #{ dclone(\#data) }
The code you have will copy the contents of the list to a new list. However, if you are storing references in the list (and you have to in order to create a two-dimensional array in Perl), the references are copied, not the objects the references point to. So when you manipulate one of these referenced objects through one list, it appears as though the other list is changing, when in fact both lists just contain identical references.
You will have to make a "deep copy" of the list if you want to duplicate all referenced objects too. See this question for some ways to accomplish this.
Given your case of a two-dimensional array, this should work:
#data_new = map { [#$_] } #data;