Your observations about the performance differences between `d = d.insert(key, value)` and `d(key) = value` are insightful. Here's a breakdown of what's happening and some guidance on your follow-up question:
Understanding the Performance Difference
- Copying Behavior: When you use `d = d.insert(key, value)`, it appears that the dictionary is being copied on each insertion. This is because you are reassigning the dictionary `d` to the result of `d.insert()`, which likely involves creating a new dictionary with the updated key-value pair. On the other hand, `d(key) = value` modifies the dictionary in place, which is more efficient because it avoids the overhead of copying the entire dictionary.
- Documentation Equivalence: The documentation might claim equivalence in terms of functionality (i.e., both methods achieve the same end result), but they are not equivalent in terms of performance due to the underlying implementation differences.
Passing a Dictionary to a Function
To update a dictionary within a function without incurring the overhead of copying, you can use the `d(key) = value` style within the function. Here's how you can achieve this:
function updateDictionary(d, key, value)
d(key) = value;
end
However, due to MATLAB's copy-on-write behavior, you need to ensure that the dictionary is modified in place. One way to do this is by using a handle class, which allows for in-place modifications.
Using Handle Class for In-Place Updates
You can create a simple handle class to wrap the dictionary:
classdef DictHandle < handle
properties
Data
end
methods
function obj = DictHandle()
obj.Data = dictionary();
end
function insert(obj, key, value)
obj.Data(key) = value;
end
end
end
Now, you can pass an instance of `DictHandle` to your function:
function updateDictionary(dHandle, key, value)
dHandle.insert(key, value);
end
% Usage
dHandle = DictHandle();
updateDictionary(dHandle, 'key1', 42);
disp(dHandle.Data)
The performance difference you observed is due to how `d = d.insert(...)` likely involves copying, whereas `d(key) = value` modifies the dictionary in place. By using a handle class, you can ensure that dictionary updates occur in place, avoiding unnecessary copying and improving performance. This approach should give you the speed and flexibility you need without switching to `containers.Map`.
I hope this helps!
