[R] Reference a variable inside a string and another for object assingments

[MacQueen, Don]

I sometimes do this sort of thing with "tricks" like this:

  sql <- "select * from mytable where dt >= 'ADATE'"

  dbGetQuery( con, gsub('ADATE', '2012-06-12 23:14', sql) )



Or if mydates is a vector of dates stored as a POSIXt object:

for (id in mydates) {
 dbGetQuery( con,  gsub('ADATE', format(id), sql) )
}


-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 8/16/12 12:30 PM, "Kenneth Rose" <kennethrose82 at gmail.com> wrote:

>Hi R community
>
>I copied a bit of my R code that gets some data from a database. You
>won't be able to run the code, but I am a beginner so you will
>probably understand what going on.
>
>I would like to make a variable I can refer to inside the sqlQuery.
>Instead of writing the start date and time (ex SP.lokaldatotid >=
>'2005-01-01 00:00:00') inside the query I would like to define it in
>the beginning of the code, so I don't have to fiddle with a lot of
>dates each time I wan't to change it. I would like to do this for a
>few of the variables and maybe even make a list/array I can loop
>through, so I don't have to write the same code multiple times (for
>SYS and DK1).
>
>I have searched for a solution for two days now, but I am not sure
>what it's called and are probably writing the wrong queries :-)
>
>
>Thank you for your help!
>
>Kenneth
>
>My code:
>
>library(xts)
>library(RODBC)
>
>
>#Define channnel (i configured my own SYSTEM-DNS, via ODBC)
>ch <- odbcConnect("DI2")
>
>#####################################################################
>############################## GET DATA    ##########################
>#####################################################################
>
>############################## SYSTEM spot ##########################
># Hent data fra SQL Server
>sys <- sqlQuery (ch, paste("SELECT  SP.lokaldatotid, SP.pris FROM
>DataIndsamling2.dbo.SpotPriser SP",
>                           "WHERE (SP.omraade_id= 0 AND
>SP.lokaldatotid >= '2005-01-01 00:00:00')"))
>#Definer dato og tid kolonne
>sys$lokaldatotid <- as.POSIXct(sys$lokaldatotid)
>
>#Make a XTS object
>sys_xts <- xts(sys[,-1], order.by=sys[,1])
>
># Recalculate data from hours to daily, monthly and yearly averages
>sys_xts_daily <- apply.daily(sys_xts, FUN=mean)
>sys_xts_monthly <- apply.monthly(sys_xts, FUN=mean)
>sys_xts_yearly <- apply.yearly(sys_xts, FUN=mean)
>
>
>############################## DK1 spot #############################
># Hent data fra SQL Server
>dk1 <- sqlQuery (ch, paste("SELECT  SP.lokaldatotid, SP.pris FROM
>DataIndsamling2.dbo.SpotPriser SP",
>                           "WHERE (SP.omraade_id= 5 AND
>SP.lokaldatotid >= '2005-01-01 00:00:00')"))
>#Definer dato og tid kolonne
>dk1$lokaldatotid <- as.POSIXct(dk1$lokaldatotid)
>
>#Lav om til xts object
>dk1_xts <- xts(dk1[,-1], order.by=dk1[,1])
>
>#Data omregnet fra time ->> daglig, måned, årlige gennemsnit
>dk1_xts_daily <- apply.daily(dk1_xts, FUN=mean)
>dk1_xts_monthly <- apply.monthly(dk1_xts, FUN=mean)
>dk1_xts_yearly <- apply.yearly(dk1_xts, FUN=mean)
>
>______________________________________________
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