Updating containers.Map with a new containers.Map - does new key overwrite old?

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Nathan Thern 2018-8-31

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/417040-updating-containers-map-with-a-new-containers-map-does-new-key-overwrite-old

I refer to the Read and Write Using Key Index documentation.

A new containers.Map can be created by combining two containers.Map:

m1 = containers.Map({1, 5, 8}, {'A', 'B', 'C'});
m2 = containers.Map({8, 9, 6}, {'X', 'Y', 'Z'});
m = [m1; m2];
keys(m), values(m)
ans = 
    [1]    [5]    [6]    [8]    [9]
ans = 
    'A'    'B'    'Z'    'X'    'Y'

Note that value 'C' for key 8 was overwritten. In the same way I could update Map m1 with the key/value pairs in m2:

m1 = [m1; m2];
keys(m1), values(m1)
ans = 
    [1]    [5]    [6]    [8]    [9]
ans = 
    'A'    'B'    'Z'    'X'    'Y'

What I would like to know (the documentation isn't clear on this) is:

Is it guaranteed that the value in m2 will overwrite any duplicate key values from m1.

I could take the question a step further with this example:

m1 = containers.Map({1, 5, 8}, {'A', 'B', 'C'});
m2 = containers.Map({8, 9, 6}, {'X', 'Y', 'Z'});
m3 = containers.Map({2, 8, 3}, {'Q', 'R', 'S'});
m1 = [m1; m2; m3];
keys(m1), values(m1)
ans = 
    [1]    [2]    [3]    [5]    [6]    [8]    [9]
ans = 
    'A'    'Q'    'S'    'B'    'Z'    'R'    'Y'