Function with dplyr, tidyr and ggplot - r

Question

How can I make a function that takes a column and uses that in dplyr, tidyr and ggplot?
df <- data.frame(date_col = c(1,1,2,2,3,4,4,5,5),
col_a = c('a','b','a','b','a','a','b','a','b'),
val_col = runif(9))
How do I write a function takes a parameter param_col instead of the hardcoded col_a
df %>%
group_by(date_col, col_a) %>%
summarise(val_col = sum(val_col)) %>%
complete(col_a, date_col) %>%
ggplot(aes(date_col, val_col, color = col_a)) +
geom_line()
The dplyr and ggplot calls work in the code outlined below. But how should the complete call be written? Or should complete_ be used?
Is there a more canonical way of doing this?
plot_nice_chart <- function(df, param_col) {
enq_param_col <- enquo(param_col)
str_param_col <- deparse(substitute(param_col))
# aggregate data based on group_by_col,
# explicitly fill in NA's for missing to avoid interpolation
df %>%
group_by(!!enq_param_col, date_col) %>%
summarise(val_col = sum(val_col)) %>%
complete(<what-should-be-here?>, date_col) %>%
ggplot(aes_string("date_col", "val_col", color = str_param_col)) +
geom_line()
}

Answer 1

The development version of tidyr, tidyr_0.6.3.9000, now uses tidyeval, so if you want to update to that you could use !! as you did in group_by.
plot_nice_chart <- function(df, param_col) {
enq_param_col <- enquo(param_col)
str_param_col <- deparse(substitute(param_col))
str_param_col
df %>%
group_by(!!enq_param_col, date_col) %>%
summarise(val_col = sum(val_col)) %>%
ungroup() %>%
complete(!!enq_param_col, date_col) %>%
ggplot(aes_string("date_col", "val_col", color = str_param_col)) +
geom_line()
}
Using the current version, you can use complete_ with variables as strings.
plot_nice_chart <- function(df, param_col) {
enq_param_col <- enquo(param_col)
str_param_col <- deparse(substitute(param_col))
df %>%
group_by(!!enq_param_col, date_col) %>%
summarise(val_col = sum(val_col)) %>%
ungroup() %>%
complete_( c(str_param_col, "date_col") ) %>%
ggplot(aes_string("date_col", "val_col", color = str_param_col)) +
geom_line()
}