如何仅合并向量-Matlab

Question

How do I combine all the vectors in small subsets of vectors in Matlab?

a= [5 6 7] b = [8 9 10] c=[11 12 13] d=[14 15 16] e=[17 18 19]

a combine with b and c:

Outcome:

M1= [ 5 6 7 8 9 10 11 12 13]

a with b and d:

M2 = [5 6 7 8 9 10 14 15 16]

and so on .....

Answer 1

This answer covers the case for an arbitrary number of vectors . The vectors are assumed to be row vectors of equal length.

Let your example data be defined as

a = [5 6 7]; b = [8 9 10]; c = [11 12 13]; d = [14 15 16]; e = [17 18 19];
vectors = {a, b, c, d, e}; %// cell array with any number of row vectors of equal size
n = 3; %// desired subset size

Then: generate all combinations of indices, use that to index into vectors , concatenate into one big row vector, and reshape that to obtain the desired result:

combs = nchoosek(1:numel(vectors), n);
result = reshape([vectors{combs.'}], numel(vectors{1})*n, []).';

This gives a matrix whose first row is your M1 , second row is M2 etc:

result =
     5     6     7     8     9    10    11    12    13
     5     6     7     8     9    10    14    15    16
     5     6     7     8     9    10    17    18    19
     5     6     7    11    12    13    14    15    16
     5     6     7    11    12    13    17    18    19
     5     6     7    14    15    16    17    18    19
     8     9    10    11    12    13    14    15    16
     8     9    10    11    12    13    17    18    19
     8     9    10    14    15    16    17    18    19
    11    12    13    14    15    16    17    18    19

Answer 2

You can use the cat function:

res = cat(2,a,b,c);

or simply the [] syntax:

res = [a b c];

In both cases, res will contain [5 6 7 8 9 10 11 12 13] .

Best,

Answer 3

Use nchoosek .

a = [5 6 7]; b = [8 9]; c = [11 12 13]; d = [14 15 16]; e = [17 18 19];
N = 3;
x = {a,b,c,d,e};
y = nchoosek(x,N);

And you have all the combination of your arrays taken N at a time in a cell array. Each row i of the cell x is a combination, so to have it back as a row vector just do

horzcat(y{i,:})

Or, if you want to get them all and put them in a cell array of size n_combs

n_combs = size(y,1);
out = cell(0,n_combs);
for i = 1 : n_combs
    out{i} = horzcat(1, y{i,:});
end

There is no constraint on the size of the arrays that you want to combine, eg, you can combine

a = [5 7]; b = [8 9]; c = [11]; d = [20 14 15 16]; e = [17 18 19];

However, if you must put together all the combination in a matrix, then the arrays have to be of the same size. In this case Luis Mendo's answer does the job.

Finally, if repetitions are allowed use nmultichoosek instead of nchoosek .