calling variable name of a dataframe inside functions in R using "$"

Question

I have a dataframe(master) that has some variables which i have stored in the list below:

cont<-list("Quantity","Amt_per_qty","Trans_tax","Total_trans_amt")
catg<-list("Gender","Region_code","SubCategory")

I am trying to create a function where I can access the variables from dataframe and perform some function on them, though x and val in below function seems to resolve, how can I access the variables using the $ sign inside function

univar<-function (x){
                 for (val in cont){
                   print (val)
                   n<-nrow(x$val) }

                      print (n)  }
univar(master)

Its returning NULL, I tried even with n<-nrow(x[,val]), that also don't seem to work.

Use [[ instead of $

akrun
– akrun

2016-12-02 10:17:10 +00:00
Commented Dec 2, 2016 at 10:17 — akrun
– akrun, Commented Dec 2, 2016 at 10:17
not working either (

muni
– muni

2016-12-02 10:18:48 +00:00
Commented Dec 2, 2016 at 10:18 — muni
– muni, Commented Dec 2, 2016 at 10:18
You have a list, you need c

akrun
– akrun

2016-12-02 10:19:56 +00:00
Commented Dec 2, 2016 at 10:19 — akrun
– akrun, Commented Dec 2, 2016 at 10:19
nrow(x) or length(x[[val]])

joel.wilson
– joel.wilson

2016-12-02 10:20:15 +00:00
Commented Dec 2, 2016 at 10:20 — joel.wilson
– joel.wilson, Commented Dec 2, 2016 at 10:20

joel.wilson · Accepted Answer · 2016-12-02 10:19:40Z

2

  i) x[val] returns a data.frame
 ii) x[,val,drop = TRUE] returns a vector
iii) x[[val]] shall return as a vector. Advantage of this is : it also works with data.tables

n <- nrow(x) or length(x[[val]])

answered Dec 2, 2016 at 10:19

joel.wilson

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Comments

akrun · Accepted Answer · 2016-12-02 10:20:42Z

0

The reason is that the OP created a list, it could be unlisted and then use [

cont <- unlist(cont)
univar<-function(x){
             for (val in cont){
               print (val)
               n<-nrow(x[[val]]) }

                  print (n)  }
univar(master)

answered Dec 2, 2016 at 10:20

akrun

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