You probably mean indexing. For example
Names={'John', 'Peter','Terry','Alice','Mary'};
ind=[3 1 4 2];
SelectedNames=Names(ind)
It's better to use double array (like the variable 'ind' in the above code) than cell array for your 'a' variable if it contains scalar numerical value in every cell. If you have to use cell array, you can use
a=num2cell(1:5)
