For-Loop Alternative for Faster Code Execution

Suppose,

a{1}=[1 6;
      1 9;
      1 8;
      3 7;
      3 0;
      4 0;
      5 0;
      5 0;
      5 0;
      5 0;]

    desired_answer{1}=   [1 6;
                          1 6;
                          1 6;                        
                          3 9;
                          3 9;
                          4 8;
                          5 7;
                          5 7;
                          5 7;
                          5 7;]

Is there a more efficient way I can do this without having to use for loop? (Cell Array is used because it is adapted from my problem)

[Matthew Eicholtz]

Can you provide more details? Here is what I conclude from your description: the number of nonzero entries in the second column equals the number of unique values in the first column; then, you want to assign each of the second-column values to all instances of the appropriate first-column value, in order. Is that correct?

[RDG]

The value "6" in column 2 should be assigned to value "1" in column 1, "9" to "3", "8" to "4", "7" to "5".

Answer 1

[Matthew Eicholtz]

Still unsure about your problem setup, but the following code will yield your desired result for the example above.

[~,~,idx] = unique(a{1}(:,1));
a{1}(:,2) = a{1}(idx,2);

Answer 2

[Matthew Eicholtz]

And if the for loop you are concerned about is looping through the cells in your cell array, then try this code:

[~,~,idx] = cellfun(@(x) unique(x(:,1)),a,'uni',0);
a = cellfun(@(x,y) [x(:,1) y],a,cellfun(@(z,i) z(i,2) ,a,idx,'uni',0),'uni',0);

Perhaps this is not the most elegant solution, in which case I expect the MATLAB pros will chime in shortly.