使用矩阵逻辑索引A（I）= B的Matlab错误

Question

Trying to do a matrix logical indexing, but Matlab seems to be crazy, what I'm missing here?

Look:

>> A
A =
   NaN   NaN   NaN   NaN
>> B
B =
     1     2     3     4
>> I
I =
     1     1     0     0
>> A(I) = B
In an assignment  A(I) = B, the number of elements in B and I must
be the same. 
>> numel(B)
ans =
     4
>> numel(A)
ans =
     4

Answer 1

Rest assured, MATLAB isn't crazy. B has 4 elements as you've shown and A(I) only has 2 because I only has 2 true values.

numel(B)
%   4

numel(A(I))
%   2

You are trying to assign 4 elements into two elements in A is which is exactly what your error states.

In an assignment A(I) = B, the number of elements in B and I must be the same

You can only assign two values from B into A with your specific value if I . I'm guessing you would want to only assign the corresponding elements of B like this.

A(I) = B(I);