[R] Create macro_var in R

[David Winsemius]

> On Feb 3, 2016, at 11:57 AM, Amoy Yang via R-help <r-help at r-project.org> wrote:
> 
> Right! the following works to r but not sqldf.
> MVAR <- "population"
> tab[[ MVAR ]]
> sqldf("select tab[[MVAR]] from tab") 

If ypu need a string to pass to sqldf, then use the `paste` function to build a single string:

sqldf( paste("select",  MVAR, " from tab") )

-- 
David.


> 
>    On Wednesday, February 3, 2016 1:18 PM, Amoy Yang via R-help <r-help at r-project.org> wrote:
> 
> 
> First, MVAR<-c("population) should be the same as "population'". Correct?
> You use tab[[MVAR]] to refer to "population" where double [[...]] removes double quotes "...", which seemingly work for r-code although it is tedious in comparison direct application in SAS %let MVAR=population. But it does not work for sqldef in R as shown below.
> 
>> key<-"pop"
>> library(sqldf)
>> sqldf("select grade, count(*) as cnt, min(tab[[key]]) as min, 
> + max(pop) as max, avg(pop) as mean, median(pop) as median,
> + stdev(pop) as stdev from tab group by grade")
> Error in sqliteSendQuery(con, statement, bind.data) : 
>   error in statement: near "[[key]": syntax error
> 
> 
> 
> 
>     On Wednesday, February 3, 2016 12:40 PM, "ruipbarradas at sapo.pt" <ruipbarradas at sapo.pt> wrote:
> 
> 
> Hello,
> 
> You can't use tab$MVAR but you can use tab[[MVAR]] if you do MVAR <- "population" (no need for c()).
> 
> Hope this helps,
> 
> Rui Barradas
>  Citando Amoy Yang via R-help <r-help at r-project.org>:
> population is the field-name in data-file (say, tab). MVAR<-population takes data (in the column of population) rather than field-name as done in SAS:  %let MVAR=population;
> In the following r-program, for instance, I cannot use ... tab$MVAR...or simply MVAR itself since MVAR is defined as "population" with double quotes if using MVAR<-c("population")
> 
>    On Wednesday, February 3, 2016 11:54 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
> 
> 
> On 03/02/2016 12:41 PM, Amoy Yang via R-help wrote:
>   There is a %LET statement in SAS: %let MVAR=population; Thus, MVAR can be used through entire program.
> In R, I tried MAVR<-c("population"). The problem is that MAVR comes with double quote "...." that I don't need. But MVAR<-c(population) did NOT work out. Any way that double quote can be removed as done in SAS when creating macro_var?
> Thanks in advance for helps!
> R doesn't have a macro language, and you usually don't need one.
> 
> If you are only reading the value of population, then
> 
> MAVR <- population
> 
> is fine.  This is sometimes the same as c(population), but in general
> it's different:  c() will remove some attributes, such as
> the dimensions on arrays.
> 
> If you need to modify it in your program, it's likely more complicated. 
> The normal way to go would be to put your code in a function, and have
> it return the modified version.  For example,
> 
> population <- doModifications(population)
> 
> where doModifications is a function with a definition like
> 
> doModifications <- function(MAVR) {
>     # do all your calculations on MAVR
>     # then return it at the end using
>     MAVR
> }
> 
> Duncan Murdoch
> 
> 
> 
>         [[alternative HTML version deleted]]
> 
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> 
>  
> 
>   
>     [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius
Alameda, CA, USA