[R] Create macro_var in R

[Duncan Murdoch]

On 03/02/2016 1:23 PM, Amoy Yang wrote:
> 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")

In that case, you can use

MVAR <- "population"

and then work with

tab[[MVAR]]

instead of tab$population.

But it would often make more sense to extract that column into a 
separate variable, and work with that, either as

MVAR <- tab$population

or

tab$population <- doModifications(tab$population)

following the same patterns as below.

Duncan Murdoch

>
>      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
>
>
>