Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down at the end of May, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: Using a loop to calculate vector differences


From   "Heidi M Pitts" <hpitts@unm.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Using a loop to calculate vector differences
Date   Fri, 21 Sep 2012 09:12:26 -0600

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

}


*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/

Heidi M. Pitts
Graduate Student
Department of Economics
University of New Mexico

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index