dplyr: Standard evaluation and enquo()

I heard standard evaluation is not recommended in dplyr, and we can do similar thing with enquo() and quo().

My original code (simplified) is

my_function <- function(data, x="OriginalX", y="OriginalY"){
  data %>%
     mutate_(CopyX = x, CopyY = y)
}

and it works.

I tried following code

my_function <- function(data, x="OriginalX", y="OriginalY"){
  qx <- enquo(x)
  qy <- enquo(y)
  data %>%
     mutate(CopyX = (!!qx), CopyY = (!!qy))
}

Why it does not work? And should we keep using standard evaluation?

The idea behind tidyeval is specifically that you don't need to put your column name between "". So this should work:

my_function <- function(data, x= OriginalX , y= OriginalY ){
  qx <- enquo(x)
  qy <- enquo(y)
  data %>%
    mutate(CopyX = !!qx,
           CopyY = !!qy)
}

Note that the !!qx and !!qy don't need to be between parenthesis

my_function(iris, Sepal.Length, Species) %>%
  head()
  Sepal.Length Sepal.Width Petal.Length Petal.Width Species CopyX  CopyY
1          5.1         3.5          1.4         0.2  setosa   5.1 setosa
2          4.9         3.0          1.4         0.2  setosa   4.9 setosa
3          4.7         3.2          1.3         0.2  setosa   4.7 setosa
4          4.6         3.1          1.5         0.2  setosa   4.6 setosa
5          5.0         3.6          1.4         0.2  setosa   5.0 setosa
6          5.4         3.9          1.7         0.4  setosa   5.4 setosa

If you need to use strings in the function parameters, you can use the ensym function to convert them:

my_function <- function(data, x= "OriginalX" , y= "OriginalY" ){
  qx <- ensym(x)
  qy <- ensym(y)
  data %>%
    mutate(CopyX = !!qx,
           CopyY = !!qy)
}

my_function(iris, "Sepal.Length", "Species") %>%
  head()
  Sepal.Length Sepal.Width Petal.Length Petal.Width Species CopyX  CopyY
1          5.1         3.5          1.4         0.2  setosa   5.1 setosa
2          4.9         3.0          1.4         0.2  setosa   4.9 setosa
3          4.7         3.2          1.3         0.2  setosa   4.7 setosa
4          4.6         3.1          1.5         0.2  setosa   4.6 setosa
5          5.0         3.6          1.4         0.2  setosa   5.0 setosa
6          5.4         3.9          1.7         0.4  setosa   5.4 setosa