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From |
Ulrich Kohler <[email protected]> |

To |
[email protected] |

Subject |
Re: st: two questions about matrix operations |

Date |
Wed, 5 Jan 2005 09:44:23 +0100 |

Katsuhide Isa wrote: > I have two questions about matrix operations in Stata. > Suppose there is a matrix form data set like below: > > A B C D > A 0 0 0 1 > B 0.3 0 0 0.7 > C 0.2 0.15 0.65 0 > D 0.3 0.4 0 0.3 > > Question 1. > To compute sum of numbers of zeros for this matrix, I wrote > the following: > > foreach var of varlist A-D{ > count if `var' == 0 > } > > The result is: > > 1 > 2 > 3 > 1 > > Namely, numbers of zeros for each variable are vertically > shown. > One step further, I'd like to obtain total sum of numbers > of zeros (1+2+3+1=7 in this case). > Is it possible to do so? In Stata, the term matrix is used for objects accessible with the various subcommands of the command -matrix-. Therefore, strictly speaking, you do not have a matrix, but a dataset. However, the answer to your question is "yes". There are many ways to do it. Here is one to start with: foreach var of varlist A-D{ count if `var' == 0 local sum = `sum' + r(N) } di `sum' > Question 2. > To compute sum of row variances, I wrote the following: > > /* sum of row variances */ > loc egen sd = rsd(A-D) > loc egen v = sd^2 > loc egen sumv = sum(v) > di in gr " sum of row variances" _col(38) ": " %5.3f in ye `sumv' > > While no errors are shown, the result for `sumv' are not > shown, either. > # Only the title "sum of row variances : " is shown. > > I don't know why this happens, thoguh I may have made some > elementary mistakes. You have used "local" in front of your -egen- commands. I am not sure why you did this. However what in effect you did is to store all the egen commands in local macros. Try out . local egen sumv = sum(v) . display "`egen'" to see what happened. > Is there any alternatives to compute? . egen sd = rsd(A-D) . gen sumv = sum(sd^2) . di sumv[_N] -- [email protected] +49 (030) 25491-361 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**st: Re: two questions about matrix operations***From:*"Katsuhide Isa" <[email protected]>

**References**:**st: two questions about matrix operations***From:*"Katsuhide Isa" <[email protected]>

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