deep-copy | 易学教程

deep copying a graph structure

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问题 I have a graph class with Node's, where each Node can connect to others: public class Node { List<Node> connections; } I would like to make a deep copy of the entire graph. As a first attempt, I tried making a copy constructor like: public Node(Node other) { connections = new ArrayList<Node>(); for (Node n : other.connections) { connections.add(new Node(n)); } } So deep copying a graph would just be: public Graph deepCopy () { Graph g = new Graph(); g.nodes = new ArrayList<Node>(); for (Node

python Pandas DataFrame copy(deep=False) vs copy(deep=True) vs '='

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Could somebody explain to me a difference between df2 = df1 df2 = df1.copy() df3 = df1.copy(deep=False) I have tried all options and did as follows: df1 = pd.DataFrame([1,2,3,4,5]) df2 = df1 df3 = df1.copy() df4 = df1.copy(deep=False) df1 = pd.DataFrame([9,9,9]) and returned as follows: df1: [9,9,9] df2: [1,2,3,4,5] df3: [1,2,3,4,5] df4: [1,2,3,4,5] So, I observe no difference in the output between .copy() and .copy(deep=False) . Why? I would expect one of the options '=', copy(), copy(deep=False) to return [9,9,9] What am I missing please? If you see the object IDs of the various DataFrames

Java HashMap - deep copy

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I am just trying to find out the best solution how to make a deep copy of HashMap . There are no objects in this map which implement Cloneable . I would like to find better solution than serialization and deserialization. stealthjong Take a look at Deep Cloning , on Google Code you can find a library. You can read it on https://github.com/kostaskougios/cloning . How it works is easy. This can clone any object, and the object doesnt have to implement any interfaces, like serializable. Cloner cloner = new Cloner(); MyClass clone = cloner.deepClone(o); // clone is a deep-clone of o Be aware

How can I make a deepcopy of a function in Python?

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I would like to make a deepcopy of a function in Python. The copy module is not helpful, according to the documentation , which says: This module does not copy types like module, method, stack trace, stack frame, file, socket, window, array, or any similar types. It does “copy” functions and classes (shallow and deeply), by returning the original object unchanged; this is compatible with the way these are treated by the pickle module. My goal is to have two functions with the same implementation but with different docstrings. def A(): """A""" pass B = make_a_deepcopy_of(A) B.__doc__ = """B"""

Python: Implementation of shallow and deep copy constructors

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问题 It is in most of the situations easy to implement copy constructors (or overloaded assignment operator) in C++ since there is a concept of pointers. However, I'm quite confused about how to implement shallow and deep copy in Python. I know that there are special commands in one of the libraries but they don't work on classes that you have written by yourself. So what are the common ways to implement? P.S. Showing process on some basic data structures (linked list or tree) will be appreciated.

Why and when to use angular.copy? (Deep Copy)

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问题 I've been saving all the data received from services direct to local variable, controller, or scope. What I suppose would be considered a shallow copy, is that correct? Example: DataService.callFunction() .then(function(response) { $scope.example = response.data; }); Recently I was told to use angular.copy in order to create a deep copy. $scope.example = angular.copy(response.data); However, the deep copy information seems to be working in the same way when used by my Angular application. Are

Is it fine to use JSON.stringify for deep comparisons and cloning?

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问题 After attempting several implementations for deep comparison and copying for JSON-serializable objects, I've noticed the fastest often are just: function deep_clone(a){ return JSON.parse(JSON.stringify(a)); }; function is_equal(a,b){ return JSON.stringify(a) === JSON.stringify(b); }; I feel like this is cheating, though. Like I'll find some problem that will annoy me on future. Is it fine to use those? 回答1: JavaScript does not guarantee the order of keys. If they are entered in the same order

Move Constructor vs Copy Elision. Which one gets called?

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问题 I have two pieces of code here to show you. They are two classes and each one provides a Move Constructor and a function which returns a temporary. In the first case, the function returning a temporary calls the Move Constructor In the second case, the function returning a temporary just tells the compiler to perform a copy elision I'm confused: in both cases I define a Move Constructor and a random member function returning a temporary. But the behavior changes, and my question is why . Note

Merge JS objects without overwriting

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问题 Suppose you have two objects: var foo = { a : 1, b : 2 }; var bar = { a : 3, b : 4 } What's the best way to merge them (and allow deep merging) to create this: var foobar = { a : [1, 3], b : [2, 4] } Edit for question clarification: Ideally, in the case of an existing property in one and not the other, I would expect an array to still be created, for normalization purposes and to allow for further reduction of the map, however the answers I'm seeing below are more than sufficient. For the

Pulling data from a CMSampleBuffer in order to create a deep copy

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问题 I am trying to create a copy of a CMSampleBuffer as returned by captureOutput in a AVCaptureVideoDataOutputSampleBufferDelegate. Since the CMSampleBuffers come from a preallocated pool of (15) buffers, if I attach a reference to them they cannot be recollected. This causes all remaining frames to be dropped. To maintain optimal performance, some sample buffers directly reference pools of memory that may need to be reused by the device system and other capture inputs. This is frequently the