deep-copy

问题 I have a long class with a lot of data members. I want to write a copy constructor for it. But, if I write my own copy constructor, I lose access to the default copy constructor. I just want to repair a few pointers in my own copy constructor. So I want to have a shallow copy of the object which can be done by the default copy constructor. Is there a possibility to access the default copy constructor when I have my own copy constructor? 回答1: Wrap the things you don't want to change in a

问题 I have (in my opinion) a strange problem with python pandas. If I do: cc1 = cc.copy(deep=True) for the dataframe cc and than ask a certain row and column: print(cc1.loc['myindex']['data'] is cc.loc['myindex']['data']) I get True What's wrong here? 回答1: Deep copying doesn't work in pandas and the devs consider putting mutable objects inside a DataFrame as an antipattern There is nothing wrong in your code, just in case if you want to know the difference with some example of deep and shallow

问题 I have (in my opinion) a strange problem with python pandas. If I do: cc1 = cc.copy(deep=True) for the dataframe cc and than ask a certain row and column: print(cc1.loc['myindex']['data'] is cc.loc['myindex']['data']) I get True What's wrong here? 回答1: Deep copying doesn't work in pandas and the devs consider putting mutable objects inside a DataFrame as an antipattern There is nothing wrong in your code, just in case if you want to know the difference with some example of deep and shallow

问题 I want to loop over a list in Python and remove particular items. I don't want to make a new list of accepted items, because in my complete example, I want to make a series of refinements to my list. Here is a simple example, in which I try to remove all numbers that are less than 3 in a list. example = [1.,2.,3.,4.,5.,6.] for e in example: if e < 3.: print "Removing:", e example.remove(e) else: print "Accepting:", e print "NAIVE:", example Removing: 1.0 Accepting: 3.0 Accepting: 4.0

问题 Let's say I have an array of integers, "orig" I want to shallow copy it, so can't I just do this: int[] shallow = orig; My professor said that for primitives, shallow and deep copy are essentially the same, in that we have to copy over each index of the array. But setting the whole array equals to another array does the same thing, right? I have a similar question with object arrays This was my ideology Book[] objArr2 = objArr1; But I was told that I would have to copy each array index over,

问题 If I create a 2D int array in Java, and then make a copy of it using Arrays.copyOf() , like so - jshell> int[][] c1 = {{1,2}, {3,4}} c1 ==> int[2][] { int[2] { 1, 2 }, int[2] { 3, 4 } } jshell> int[][] d1 = Arrays.copyOf(c1, c1.length) d1 ==> int[2][] { int[2] { 1, 2 }, int[2] { 3, 4 } } If I then change an element in the copy, why does the corresponding cell in the original 2D array get mutated in the process? jshell> d1[0][0] = 0 $21 ==> 0 jshell> d1 d1 ==> int[2][] { int[2] { 0, 2 }, int[2

问题 This question already has answers here : How to make a deep copy of Java ArrayList [duplicate] (2 answers) Closed 1 year ago . My problem is that I need to copy a list but a deep copy. When I modify the list a , I don't want to modify the list b . I use JDK11 so I could use list.copyOf but using that when I modify a , b is also modified. Am I doing something wrong? b = List.copyOf(a); System.out.println("A start:" + b.get(2).getSeating()); System.out.println("B start:" + b.get(2).getSeating()

问题 Say I have a Python class instance, here's a really simple example: class Book: def __init__(self, genre): self.genre = genre self.author = self.title = None return def assign_author(self, author_name): self.author = author_name return def assign_title(self, title_name): self.title = title_name return western_book_template = Book("Western") For various reasons, I want each class instance to be able to generate a deep copy of itself, and then perform some additional manipulation on the new

问题 I would like to make a copy of a class instance in python. I tried copy.deepcopy but I get the error message: RuntimeError: Only Variables created explicitly by the user (graph leaves) support the deepcopy protocol at the moment So suppose I have something like: class C(object): def __init__(self,a,b, **kwargs): self.a=a self.b=b for x, v in kwargs.items(): setattr(self, x, v) c = C(4,5,'r'=2) c.a = 11 del c.b And now I want to make an identical deep copy of c , is there an easy way? 回答1: Yes

问题 I would like to make a copy of a class instance in python. I tried copy.deepcopy but I get the error message: RuntimeError: Only Variables created explicitly by the user (graph leaves) support the deepcopy protocol at the moment So suppose I have something like: class C(object): def __init__(self,a,b, **kwargs): self.a=a self.b=b for x, v in kwargs.items(): setattr(self, x, v) c = C(4,5,'r'=2) c.a = 11 del c.b And now I want to make an identical deep copy of c , is there an easy way? 回答1: Yes