How to sort one array based on another of a different size

Hello,

I would like to sort one cell array A according to the order define by a separate cell array B of a smaller size. For example:

A = [a a b c c d d d d e e]
B = [d a c b e]

After sorting, array A would be:

A = [d d d d a a c c b e e]

Thank you for the help.

[Rik]

I would write code that replaced every value in your top array by the index in your second array. Then you can sort and use indexing to get the original values back.

Answer 1

[Stephen23]

As Rik wrote, the MATLAB solution is to use ismember, e.g.:

>> A = {'a','a','b','c','c','d','d','d','d','e','e'};
>> B = {'d','a','c','b','e'};
>> [X,Y] = ismember(A,B);
>> [~,Z] = sort(Y(X));
>> C = A(Z)
C =
    'd'    'd'    'd'    'd'    'a'    'a'    'c'    'c'    'b'    'e'    'e'

Answer 2

[Aakash Mehta]

A = ['a' 'a' 'b' 'c' 'c' 'd' 'd' 'd' 'd' 'e' 'e']
B = ['d' 'a' 'c' 'b' 'e']

sizeA = length(A)
sizeB = length(B)

You can use the container.Map to track the frequency of the characters. This approach will also work when A is not sorted.

M = containers.Map

for i=1:sizeA
    if isKey(M,A(i))==1
        M(A(i)) = M(A(i)) + 1;
    else
        M(A(i)) = 1;
    end
end

You will get the map M, which contains the characters as a key and frequency as their value.

Now using following code you can get the desired output.

str = "";
for i=1:sizeB
    if isKey(M,B(i))==1
        for j=1:M(B(i))
            str = strcat(str,B(i));
        end
    end
end

[Rik]

I suspect this can be vectorized with ismember. I suspect that the mapping you are proposing has a lot of unnecessary overhead.