create multiple submatrices from a large matrix

Dear All communtity members,

I want to write a code that creates multiple submatrices from a large matrix either through a loop or by vectorization.

The large matrix has a dimension of 54x7056 and I want to create 16 submatrices selected from different columns.

The submatrices shall be selected and repeated as following;

sub1= column, 1, 9 to 17, 25 to 33, 41 to 49.......................... and 7049 to 7056.

sub2= column, 1 to 2, 10 to 18,26 to 34, 42 to 50.................. and 7050 to 7056.

sub3= column, 1 to 3, 11 to 19,27 to 35, 43 to 51.................. and 7051 to 7056.

sub4= column, 1 to 4, 12 to 20, 28 to 36, 44 to 52................. and 7052 to 7056.

sub5= column, 1 to 5, 13 to 21, 29 to 37, 45 to 53.....7037 to 7045, and 7053 to 7056.

sub6= column, 1 to 6, 14 to 22, 30 to 38, 46 to 54.... 7038 to 7046, and 7054 to 7056.

sub7= column, 1 to 7, 15 to 23, 31 to 39, 47 to 55, .. 7039 to 7047, and 7055 to 7056.

sub8= column, 1 to 8, 16 to 24, 32 to 40, 48 to 56.... 7040 to 7048, and 7056.

sub9= column, 1 to 9, 17 to 25, 33 to 41, 49 to 57................... and 7041 to 7049.

sub10= column, 2 to 10, 18 to 26, 34 to 42, 50 to 58............... and 7042 to 7050.

sub11= column, 3 to 11, 19 to 27, 35 to 43, 51 to 59................ and 7043 to 7051.

sub12= column, 4 to 12, 20 to 28, 36 to 44, 52 to 60............... and 7044 to 7052.

sub13= column, 5 to 13, 21 to 29, 37 to 45, 53 to 61............... and 7045 to 7053.

sub14= column, 6 to 14, 22 to 30, 38 to 46, 54 to 62............... and 7046 to 7054.

sub15= column, 7 to 15, 23 to 31, 39 to 47, 55 to 63............... and 7047 to 7055.

sub16= column, 8 to 16, 24 to 32, 40 to 48, 56 to 64............... and 7048 to 7056.

I appreciate all help and tips.

Thanks in advance!

Answer 1

[Bruno Luong]

Probably better code using logical indexing

M = rand(54,7056);
[m,n] = size(M);

pattern = circshift([true(1,9) false(1,7)], -8);
pattern = repmat(pattern, 1, n/16);
pattern = pattern(1:n);
s = struct();
for r=1:16
    s.(sprintf('sub%d',r)) = M(:,pattern);
    pattern = circshift(pattern, 1);
end

s

[Askeladden2]

Dear Bruno,

Thank you for all your help- I really appreciate it!

Both codes are working perfectly!

Answer 2

[Bruno Luong]

M = rand(54,7056);
[m,n] = size(M);

offset = 7;
offset = mod(offset,16);
I=(-16:8:ceil(n/8)*8+offset+8);
J=-offset+(0:15)';
C = I+J;
s=struct();
for r=1:16
    a = max(C(r,1:2:end),1);
    b = min(C(r,2:2:end),n);
    if length(a)>length(b)
        a(end)=[];
    end
    c = arrayfun(@(a,b) a:b, a, b, 'unif', 0);
    c = cat(2,c{:});
    s.(sprintf('sub%d',r)) = M(:,c);
end
s

[Askeladden2]

Dear Bruno,

Thank you very much for the prompt reply.

All the 16 submatrices shall have the same dimension (54 x 3969) given the sequence and repetion provided in the text above. Just for clarifications; the large matrix (54x7056) consists of 441 individual "points" in 16 "directions". I want to extract all point for 9 of the 16 directions (i.e. 54x441*9).

When I test your code submatrix 1-4 have smaller dimensions (i.e.submatrix 1 = 54x3965,.. submatrix4= 54x3968). Do you know what might be causing this?

Kind regards.

[Bruno Luong]

With editted code

s = 

  struct with fields:

     sub1: [54×3969 double]
     sub2: [54×3969 double]
     sub3: [54×3969 double]
     sub4: [54×3969 double]
     sub5: [54×3969 double]
     sub6: [54×3969 double]
     sub7: [54×3969 double]
     sub8: [54×3969 double]
     sub9: [54×3969 double]
    sub10: [54×3969 double]
    sub11: [54×3969 double]
    sub12: [54×3969 double]
    sub13: [54×3969 double]
    sub14: [54×3969 double]
    sub15: [54×3969 double]
    sub16: [54×3969 double]