R dplyr 0.7.2 - functional programming. Resolving dataframe name - r

Question

I am writing a R function using dplyr 0.7.2 syntax to pass input and output data frame names and a column name to sort on. The following is the code I have.
#test data frame creation
lb<- data.frame(study = replicate(25,"ABC"),
subjid = c("x1","x2","x3","x4","x5"),
visit = c("SCREENING","VISIT1","VISIT2","VISIT3","EOT"),
visitn = c(-1,1,2,3,4),
param = c("ALB","AST","HGB","HCT","LDL"),
aval = replicate(5, sample(c(20:100), 1, rep = TRUE)))
#sort function- user to provide input/output df names and column name to sort on
sortdf <- function(ind,outd,col){
col <- enquo(col)
outd <- ind %>% arrange(!!col)
outd <<- outd # return dataframe to workspace
}
sortdf(lb,lb_sort, visitn)
the above code works but the output df name is not getting resolved to lb_sort. output df is named as the name of the associated parameter (outd). Need some help!
Thanks,
Prasanna

Answer 1

You do not need to make use of the << in this context. In effect, your function is a wrapper for arrange:
my_sort <- function(df, col) {
col <- enquo(col)
df %>%
arrange(!!col)
}
my_sort(df = lb, col = visitn)
Then you could create your objects as usual:
my_sort(df = lb, col = visitn) -> sorted_stuff
Edit
As per request, forcing creation of names object in parent environment.
my_sort <- function(df, col, some_name) {
col <- enquo(col)
df %>%
arrange(!!col) -> dta_a
# Gather env. inf
e <- environment() # current environment
p <- parent.env(e)
# Create object in parent env.
assign(x = some_name,
value = dta_a,
envir = p)
# If desired return another object
# return(some_other_data)
}
my_sort(df = lb, col = visitn, some_name ="created_data")
Explanation
e/p objects are used to gather information about functions current and parent environment
assign uses string and creates names object in function's parent environment. Global environment, if called as provided in the example.
Remarks
This is odd behaviour, when called as shown:
>> ls()
[1] "lb" "my_sort"
>> my_sort(df = lb, col = visitn, some_name ="created_data")
>> ls()
[1] "created_data" "lb" "my_sort"
The function leaves "created_data" object in global environment. This is inconsistent with expected behaviour where the user would usually create objects:
my_sort(df = lb, col = visitn) -> created_data
and I wouldn't encourage using it. If the actual problem is concerned with returning multiple objects a potentially better approach may involve packing all the results into a list and returning one list:
list(result_1 = mtcars,
result_2 = airquality)