# [R] data manipulation in R

Patrick Ball lookout_20005 at yahoo.com
Sun Apr 15 23:01:35 CEST 2001

```Dear List:

I have a data manipulation problem that I was unable
to solve in R.  I did it in SQL, and it may be that
the solution in R is to do it in SQL, but I wondered
if people could imagine a vector-based solution.

Imagine a list A[i] of observers who observe some set
of events B[j].  Each observer i may observe one or
more events, and each event j may have been observed
by one or more observers.  Thus the data are a
lower-triangular array AxB where each cell [i,j] has a
zero or one indicating whether observer i saw event j.

I am interested in how observers cluster in circuits
whereby observer _a_ sees events _1,2,3_, observer _b_
sees events _2,4,5_, observer _c_ sees event _4_, and
observer _d_ sees _4,6,7_.  Observers a, b, c, d
comprise a circuit linked by the events they jointly
observed.

Given AxB, how can we use R to articulate the
circuits?  Pseudocode for my SQL solution is below.

For each observation i:
- get all the events [j1,j2,...jk] observed by i
- get all the observations [i_m] which observe one or
more events in  [j1,j2,...jk]
- count [i_m]
- assign events [i_m] to i's circuit if i_m > i
- end

What would an R solution look like?  The "get all the"
and the "assign events" are pure SQL reasoning
(select, update).

Best.

- PB

Patrick Ball, PhD.
Deputy Director
AAAS Science and Human Rights Program
http://shr.aaas.org

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```