RE: st: Transform matrices

[Nick Cox <n.j.cox@durham.ac.uk>]

For completeness, note that a pre-Mata program was published in STB-56 in 2000 for this purpose:

STB-56  dm79  . . . . . . . . . . . . . . . . . . Yet more new matrix commands
        (help matcorr, matewmf, matvsort, svmat2 if installed)  . .  N. J. Cox
        7/00    pp.4--8; STB Reprints Vol 10, pp.17--23
        commands to produce a correlation matrix, elementwise monadic
        function of another matrix, selected subsets of matrix rows
        and columns, vec or vech of a matrix, elements sorted within
        a vector, matrix from a vector, and commands to save matrices
        see mata matrix language incorporated into Stata 9.0

The program is called -matvtom-. Its main interest is for any users of Stata 6,7,8 out there, but it should still work. 

For other such extras, see 

STB-50  dm69  . . . . . . . . . . . . . . . . . .  Further new matrix commands
        (help matdelrc, matewm, matmad, matpow if installed)  . . .  N. J. Cox
        7/99    pp.5--9; STB Reprints Vol 9, pp.29--34
        collection of new matrix commands providing additional matrix
        checking, management, element-wise operators, maximum absolute
        difference, and power

STB-39  dm49  . . . . . . . . . . . . . . . . . . . . Some new matrix commands
        (help matfunc, varfunc if installed)  . . . . . . . . . . .  J. Weesie
        9/97    pp.17--20; STB Reprints Vol 7, pp.43--48
        collection of new matrix commands; several for explicit matrices
        and a few for implicit matrices (i.e., variables)
        see mata matrix language incorporated into Stata 9

Nick 
n.j.cox@durham.ac.uk 

Tirthankar Chakravarty
======================

More generally, you can use selection vectors:

clear*
mat define A = (1, 2, 3, 4, 5, 6)'
mata
mA = st_matrix("A")
st_matrix("B", (mA[2:*(1::length(mA)/2):-1,1], ///
	mA[2:*(1::length(mA)/2),1]))
end
mat list B

Tirthankar Chakravarty
======================

> Using the Mata -rowshape()- function:
>
> *************************************
> clear*
> mat define A = (1, 2, 3, 4, 5, 6)'
> mata: st_matrix("B", rowshape(st_matrix("A"), 3))
> mat list B
> *************************************

Ulrich Atz
==========

>> I tried to get a column vector into a matrix format, such as
>>
>> 1
>> 2
>> 3
>> 4
>> 5
>> 6
>>
>>  into
>>
>> 1       2
>> 3       4
>> 5       6
>>
>> for a general specification.
>>
>> My clumsy solution was to create two loops
>>
>> clear
>> mat def A = (1\ 2\ 3\ 4\ 5\ 6)
>>
>> forvalues n = 1(2)5 {
>>        mat a`n' = A[`n', 1]
>>        if `n' == 1     local m = "`n'"
>>                else local m = "`m' \ `n'"
>>        mat c1 = (`m')
>> }
>>
>> forvalues n = 2(2)6 {
>>        mat a`n' = A[`n', 1]
>>        if `n' == 2     local k = "`n'"
>>                else local k = "`k' \ `n'"
>>        mat c2 = (`k')
>> }
>>
>> mat B = (c1, c2)
>>
>> mat list B
>>
>>
>> Surely there is a more elegant (and more general) way? Perhaps Mata is the solution?
>>
>> This is a rather academic exercise, but it would be nice if someone could share his/her potential code example.

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