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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 > > } > * * 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/

**Follow-Ups**:**Re: st: Using a loop to calculate vector differences***From:*"Heidi M Pitts" <hpitts@unm.edu>

**References**:**st: Using a loop to calculate vector differences***From:*"Heidi M Pitts" <hpitts@unm.edu>

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