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| From | Nick Cox <njcoxstata@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: Using a loop to calculate vector differences |
| Date | Fri, 21 Sep 2012 00:59:15 +0100 |
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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