arrange_() multiple columns with descending order

Question

I am trying to use arrange_() with string input and in one of the columns in descending order.

library(dplyr) # R version 3.3.0 (2016-05-03) , d         


        

Answer 1

We can paste 'desc' as a string to evaluate it.

myCol1 <- paste0("desc(", "x)")
df1 %>% 
     arrange_(.dots = c("grp", myCol1))
#  grp    x
#1   1 6.16
#2   1 3.39
#3   1 2.82
#4   2 9.17
#5   2 4.35

Or with 'myCol'

df1 %>% 
      arrange_(.dots = c("grp", paste0("desc(", myCol, ")")))

Or use lazyeval

library(lazyeval)
df1 %>%
     arrange_(.dots = c("grp", interp(~ desc(n1), n1 = as.name(myCol))))
#  grp    x
#1   1 6.16
#2   1 3.39
#3   1 2.82
#4   2 9.17
#5   2 4.35

---

By using "desc(myCol)", it is a single string and the value of the 'myCol' is not evaluated.

Update

Or another option is parse_expr (from rlang) and evaluate with !!

df1 %>%
    arrange(grp, !! rlang::parse_expr(myCol1))
#grp    x
#1   1 6.16
#2   1 3.39
#3   1 2.82
#4   2 9.17
#5   2 4.35

---

Or using the original string in the OP's post. Convert the string to symbol (sym), evaluate (!!) and arrange it in descending (desc) order

myCol <- "x"
df1 %>% 
    arrange(grp, desc(!! rlang::sym(myCol)))
# grp    x
#1   1 6.16
#2   1 3.39
#3   1 2.82
#4   2 9.17
#5   2 4.35