Re: st: Using a loop to calculate vector differences

["Heidi M Pitts" <hpitts@unm.edu>]

Thank you very much.  I will try both suggestions.

Many thanks.
Heidi

On Fri, 21 Sep 2012 00:59:15 +0100
 Nick Cox <njcoxstata@gmail.com> wrote:
> As you want to use Stata's matrix language, a program 
> -matgop-
> published in 1999 is a direct solution. See dm69 and as 
> context a
> prequel and a sequel.
>
> 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
> 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
> You can get clickable links to install by typing
>
> . search matrix, historical stb
>
> The code could be
>
> . mat M=[0, 0, 0, 0, 0, 0, 0, .1, .4, .4, .1]'
>
> . mat F=[0, 0, 0, 0, 0, .05, .3, .6, .05, 0, 0]
>
> . matgop M F diff, op(-)
>
> diff[11,11]
>         c1      c2      c3      c4      c5      c6 
>     c7      c8
>  c9     c10     c11
> r1   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r2   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r3   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r4   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r5   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r6   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r7   0.000   0.000   0.000   0.000   0.000  -0.050 
> -0.300  -0.600
> -0.050   0.000   0.000
> r8   0.100   0.100   0.100   0.100   0.100   0.050 
> -0.200  -0.500
> 0.050   0.100   0.100
> r9   0.400   0.400   0.400   0.400   0.400   0.350 
>  0.100  -0.200
> 0.350   0.400   0.400
> r10   0.400   0.400   0.400   0.400   0.400   0.350 
>  0.100  -0.200
> 0.350   0.400   0.400
> r11   0.100   0.100   0.100   0.100   0.100   0.050 
> -0.200  -0.500
> 0.050   0.100   0.100
>
> Here -...gop- is generalized outer product, and the 
> generalisation
> inspired by APL
>
> http://en.wikipedia.org/wiki/APL_(programming_language)
>
> is to allow binary operators other than multiplication.
>
> In your code you loop around
>
> gen y=x_male`i'-y_female
>
> and when the macro `i' is 1 this becomes
>
> gen y = x_male1 - y_female
>
> and -- as Stata does tell you -- it can't find -x_male1- 
> (which in
> this context can _only_ be a variable with that name or 
> failing that a
> scalar with that name). You want the first element of 
> the Stata vector
> -x_male- which would be -x_male[1,1]-. So, the problem 
> is that
> -x_male1- doesn't exist, not that it is something other 
> than what you
> want.
>
> If that bug were fixed, there is another in the loop: 
> second time
> around the loop the -generate- statement would fail as 
> -y- already
> exists.
>
> Your code shows other problems, as you appear to want to 
> store a
> matrix in the variable -diff-.
>
> All that said, my reference to -matgop- is largely just 
> parental
> indulgence. It's best just to use some Mata:
>
> mata :
> M= (0, 0, 0, 0, 0, 0, 0, .1, .4, .4, .1)'
> F= (0, 0, 0, 0, 0, .05, .3, .6, .05, 0, 0)
> len = length(F)
> diff = J(0, len, .)
>
> for(j = 1; j <= len; j++) {
>        diff = diff \ (M[j] :- F)
> }
>
> diff
>           1      2      3      4      5      6      7 
>     8      9
>  10     11
>     +------------------------------------------------------------------------------+
>   1 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   2 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   3 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   4 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   5 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   6 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   7 |     0      0      0      0      0   -.05    -.3 
>   -.6   -.05
>   0      0  |
>   8 |    .1     .1     .1     .1     .1    .05    -.2 
>   -.5    .05
>  .1     .1  |
>   9 |    .4     .4     .4     .4     .4    .35     .1 
>   -.2    .35
>  .4     .4  |
>  10 |    .4     .4     .4     .4     .4    .35     .1 
>   -.2    .35
>  .4     .4  |
>  11 |    .1     .1     .1     .1     .1    .05    -.2 
>   -.5    .05
>  .1     .1  |
>     +------------------------------------------------------------------------------+
>
> Nick
>
> On Thu, Sep 20, 2012 at 10:45 PM, Heidi M Pitts 
> <hpitts@unm.edu> wrote:
> > Can anyone help fix my code for the following issue:
> >
> > I have two vectors:
> > M=[0, 0, 0, 0, 0, 0, 0, .1, .4, .4, .1]
> > F=[0, 0, 0, 0, 0, .05, .3, .6, .05, 0, 0]
> > so n=11 obs for each vector.
> >
> > I?m trying to calculate the vector difference between 
> > each element `i? in M
> > and the whole vector F.    So the first vector of 
> > differences would be [M1=0
> > minus 0,0,0,0,0,.05,.3,.6,.05,0,0].  Then I would 
> > calculate a second set of
> > differences, M2=0 - same F vector, and stack it under 
> > the diff vector.
> > I have written a simple loop to calculate each 
> > difference. But the error
> > message I get is: ?x_male1 not found?. Seems that my 
> > code is not recognizing
> > that I want the first element of M to subtract each 
> > element of F and
> > populate the vector ?diff?.  Can anyone help?  Seems 
> > that the first issue is
> > that ?x_male1? is not equal to 0, the first element in 
> > the vector.
> >
> > /************  program to calculate difference of
> > distributions***************/
> > set matsize 100
> >
> > mkmat x_male
> > mkmat y_female
> > mkmat y_fem_inv
> >
> > set obs 11
> > gen n=_n
> > gen diff=.
> > mkmat diff
> > forvalues i=1(1)11 {
> >         gen y=x_male`i'-y_female
> >         replace diff=y if `i'< n
> >
> > }
> *
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Heidi M. Pitts
Graduate Student
Department of Economics
University of New Mexico

*
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