# [R] Help to make a specific matrix

Sun Jul 10 14:36:37 CEST 2005

```In addition to Gabor's solution, you might be interested in the
combinations function from the gtools package.

library(gtools)
combinations(5,2)
[,1] [,2]
[1,]    1    2
[2,]    1    3
[3,]    1    4
[4,]    1    5
[5,]    2    3
[6,]    2    4
[7,]    2    5
[8,]    3    4
[9,]    3    5
[10,]    4    5

On Sat, 2005-07-09 at 21:42 -0300, Jose Claudio Faria wrote:
> Dear R users,
>
> The solution is probably simple but I need someone to point me to it.
> How can I to generate a matrix from a numeric sequence of 1:10 like 'A' or 'B'
> below:
>
> A)
> |--------------------|
> |      1  2  3  4  5 |
> |--------------------|
> | 1 |  0             |
> | 2 |  1  0          |
> | 3 |  2  5  0       |
> | 4 |  3  6  8  0    |
> | 5 |  4  7  9 10  0 |
> |--------------------|
>
> B)
> |--------------------|
> |      1  2  3  4  5 |
> |--------------------|
> | 1 |  0  1  2  3  4 |
> | 2 |  1  0  5  6  7 |
> | 3 |  2  5  0  8  9 |
> | 4 |  3  6  8  0 10 |
> | 5 |  4  7  9 10  0 |
> |--------------------|
>
> This question is related with the possible combinations of five objects two the
> two, i.e, C(5,2).
>
> Any help would be greatly appreciated.
>
> Regards,

```