MATLAB: How i can create a n+1 column matrix from n column matrix

Question

i have a matrix 10*n, for example, let n=3

a= [ 1     2     3
     1     2     4
     1     2     5
     1     3     4
     1     3     5
     1     4     5
     2     3     4
     2     3     5
     2     4     5
     3     4     5]

i want to create another matrix n+1

b=[1 2 3 4
   1 2 3 5
   1 2 4 5
   1 3 4 5
   2 3 4 5]

this is obtained from a as

{1 2 3} and from 
{1 2 4}

{1 2 3 4} is created, where no pair must repeat and

{1 2 3} or 
{1 2 4} or 
{2 3 4}

all pair must be present in a or delete that pair.

please please help me.

i want to know how i can obtain a 4 column matrix from 3 column matrix, if i want 5 column from 4 column matrix then where is the main change in code.

please help me.

Answer 1

It looks to me as if you need to use:

   b = nchoosek(1:5,4);