row / col concatenation when of differeng lengths

[Paul Rathouz]

this is probably completely obvious, but suppose I want a 3x2 matrix with all "1"s in the 1st column and numbers like 2,3,4 in the second column. I thought I could just type (1,(2 \ 3\ 4)), but that throws a conformability error, I could do this using the J() function for the first column, but because we do this kind of thing all the time, I thought there might be a much quicker way. is there? - P

[Joseph Coveney]

. . . I want a 3x2 matrix with all "1"s in the 1st column and numbers like 2,3,4 in the second column.

Maybe

mata
diagonal(I(3)), (2::4)

:ÿdiagonal(I(3)),ÿ(2::4)
ÿÿÿÿÿÿÿ1ÿÿÿ2
ÿÿÿÿ+---------+
ÿÿ1ÿ|ÿÿ1ÿÿÿ2ÿÿ|
ÿÿ2ÿ|ÿÿ1ÿÿÿ3ÿÿ|
ÿÿ3ÿ|ÿÿ1ÿÿÿ4ÿÿ|
ÿÿÿÿ+---------+

:

[John Mullahy]

Paul, for what it's worth I've come to increasingly appreciate the flexibility of J(., ., .) in Mata programming. Among other things the fact that its third argument can be a vector or matrix has sometimes streamlined otherwise messy programming.

mata

r1=J(3,1,1)
r2=J(1,1,J(3,1,1))

r1
r2

end

This yields

: r1=J(3,1,1)

: r2=J(1,1,J(3,1,1))

:
: r1
       1
    +-----+
  1 |  1  |
  2 |  1  |
  3 |  1  |
    +-----+

: r2
       1
    +-----+
  1 |  1  |
  2 |  1  |
  3 |  1  |
    +-----+

[Joseph Coveney]

. . . because we do this kind of thing all the time, I thought there might be a much quicker way.

I forgot to mention that if you don't want to type all that out each time, then you can just park it all into a convenient custom function.

mata:

real matrix function oar(real scalar rows) return(J(rows, 1, 1), (2::rows+1))

// or

real matrix function dar(real scalar rows) return(diagonal(I(rows)), (2::rows+1))

oar(3)
dar(3)

end

exit