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From |
"Sebastian F. Büchte" <sfbuechte@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Sum over all possible combinations |

Date |
Sat, 21 Jul 2007 09:47:58 +0200 |

On 7/21/07, J E <je_123@hotmail.com> wrote:

Dear statalisters I am interested in computing the sum of the absolute value of all possible differences within a group of my sample. Suppose that the variable "group" denotes the variable indicating the group to which an individual belongs and Y is an outcome variable. I am interested in computing sum of abs (Yi-Yj) for all i and j belonging to group K My programming skills are almost none. Can somebody help me out regarding an efficient way of computing such statistic?

Julio, I think your problem may be solved by using -joinby-. I prepared a little example to demonstrate the way I would do it: The result you are asking for can then be found in the variable sum_dy * -- begin example // begin setting up an example dataset clear set obs 10 gen group = _n tempvar expand set seed 1234567890 gen `expand' = round(uniform() * 10,1) expand `expand' gen y_i = uniform() * 10 // end setting up an example dataset bys group: gen g_i=_n tempfile join_file preserve ren y_i y_k save `join_file', replace restore joinby group using `join_file', unmatched(none) bys group: egen sum_dy = sum(abs(y_i - y_k)) // cleaning up bys group g_i: keep if _n==1 drop y_k g_i * -- end example -- Sebastian * * 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: problem with command window in Stata 10***From:*Ricardo Ovaldia <ovaldia@yahoo.com>

**References**:**st: Sum over all possible combinations***From:*"J E" <je_123@hotmail.com>

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