clssification of a data series according to its numbers

Hi all,

I have some cells like "a" whose lenght decrease each step like below:

a{1}=[1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16]';
a{2}=[1  2  3  4  5  6  7  8  9  10  11  12  13  14  15]';
a{3}=[1  2  3  4  5  6  7  8  9  10  11  12  13  14]';
a{4}=[1  2  3  4  5  6  7  8  9  10  11  12  13]';

I wanto to classify the elements of a{1} , a{2}, a{3} and a{4} to "b", "c" , "d" and "e" cells, respectively. The dominant idea for classification is the elements of "b", "c" , "d" and "e" must be a ratio of 4 as possible. The desired outputes must be in the following way:

b{1}=a{1}(1:4,1); b{2}=a{1}(5:8,1); b{3}=a{1}(9:12,1);   b{4}=a{1}(13:16,1);
c{1}=a{2}(1:4,1); c{2}=a{2}(5:8,1); c{3}=a{2}(9:12,1);   c{4}=a{2}(13:15,1);
d{1}=a{3}(1:4,1); d{2}=a{3}(5:8,1); d{3}=a{3}(9:11,1);   d{4}=a{3}(12:14,1);
e{1}=a{4}(1:4,1); e{2}=a{4}(5:7,1); e{3}=a{4}(8:10,1);   e{4}=a{4}(11:13,1);

I have written a single program for a bove question but it's too complicated.

How can I write this program as short as possible? Thanks in advance.