[R] Sampling from a Postgres database

[Joe Conway]

On 01/15/2010 01:49 AM, Bart Joosen wrote:
> 
> One way could be to first select only the unique ID's, sample this and then
> select only the relevant records:
> 
> strQuery = "SELECT ID from tblFoo;"
> IDs <- sqlQuery(channel, strQuery)
> sample.IDs <- sample(IDs,10)
> strQuery = paste("SELECT ID from tblFoo WHRE ID IN(", sample.IDs, ");")
> IDs <- sqlQuery(channel, strQuery)

Better is to use the built-in random() function in Postgres:

#select count(*) from visits;
  count
---------
 4846604
(1 row)

# select count(*) from visits where random() < 0.005;
 count
-------
 24391
(1 row)

HTH,

Joe

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