Compare elements in a matrix for a variable

Hi

I want to compare the elements in a 3D matrix (10x6x31) to a varaible I have. If they match I would like to update the matrix and output a different value in that element corresponding to a different variable.

The two varaibles are related, where the first is the id (75x1) and the r value (75x1) corresponds to this.

This is what I have attempted but it doesnt seem to wrok.

id= material_data{1,1};
r= material_data{1,2};
j = numel(M_3D);
for i = 1:j
    if M_3D(i)==id(:)
        M_3D(i)=r;
    end
end

Answer 1

[Rik]

So essentially a lookup table?

%generate some random data
id= rand(75,1);
r= rand(75,1);
id_list=unique(id);
M_3D=id_list(randi([1 numel(id_list)],10,6,31));

%using the a variable is optional
[a,index_in_id]=ismember(M_3D,id);
if ~all(a(:))
    error('missing indices')
end
replaced=r(index_in_id);

%confirm with loop
replaced2=M_3D;
for n=1:numel(replaced2)
    ind= id==replaced2(n);
    replaced2(n)=r(ind);
end
clc,assert(isequal(replaced,replaced2),'lookup failed')

[R2]

It seems this requires all of the ids to match, what if it were to look for any that do but if some dont thats ok.