Conditional Element-wise Transformation of a matrix

[Michael Howell-Moroney]

Dear Statalisters,

I am trying to do a conditional transformation of a matrix, Specifically, I want a new matrix B that returns 1/x if x>1 and x if x<1
I can do the division just fine, but do not know how to make it conditional on values of x

matrix A=(.5, .3\ 2, 5)
mata: st_matrix("B", 1 :/ st_matrix("A") )
matrix list B

My question is how can I get Mata to return 1/x for 2 and 5, but just x for .5 and .3? I have a feeling it may have to do with mm_cond, but I could not figure it out.

Thanks for your help!

Michael Howell-Moroney

[William Lisowski]

The mm_cond() function is part of the community-contributed moremata package available from SSC.

. mata:
------------------------------------------------- mata (type end to exit) ----------------------
: A = (.5, .3\ 2, 5)

: A
        1    2
    +-----------+
  1 |  .5   .3  |
  2 |   2    5  |
    +-----------+

: B = mm_cond(A:<1,1:/A,A)

: B
                 1             2
    +-----------------------------+
  1 |            2   3.333333333  |
  2 |            2             5  |
    +-----------------------------+

: end
------------------------------------------------------------------------------------------------

[Michael Howell-Moroney]

Thanks William. I can stop banging my head on the keyboard now!

Cheers

[daniel klein]

Sometimes, it is fun thinking about mathematical solutions:

A:/(A:^(2:*(A:<1)))