More tidy evaluation with ggplot2

July 3, 2018

(This article was first published on HighlandR, and kindly contributed to R-bloggers)

Following up the follow up –

After my previous post, my good friend David Henderson asked a good question on Twitter ( it happens :))


To be honest, I hadn’t even noticed there was no tilde (the ‘~’ ) in my call to facet_wrap.

So I did a little experiment :





data <- list(fdeaths,mdeaths,ldeaths) #time series data- needs prep

names(data)[1:3] <- c("fdeaths","mdeaths","ldeaths")

data <- as_tibble(data)

startdate <- as.Date('1974-1-1')

data$date <- seq.Date(startdate,by = 'month',length.out = 72)

newdata <- tidyr::gather(data, key = key, value = value,-date)

newdata$value <- as.numeric(newdata$value)
# adding in an additional colum to facet by
newdata$random <- stringr::str_sub(newdata$key,1,1)

gtest <- function(df,x,y,...) {
  # check out the ... in the function parameters
  x_quo <- enquo(x)
  y_quo <- enquo(y)
  groupvars <- quos(...) ## this is a new bit too
  p <- ggplot(df,aes(x = !!x_quo, y = !!y_quo)) +   #bangin'   
    geom_line(colour = "blue", group = 1) + 
    geom_point(colour = "blue") +
    facet_wrap(groupvars, ncol = 2) #look Ma, no tilde. Also, 2 cols, not 3
  p <- p + ggtitle(label = "Easy Tidy Eval in ggplot 3.0.0",
                   subtitle = "ggplot with tidy evaluation & facetting with no strings")
  p <- p + labs(x = NULL, y = NULL, caption = "") +



Pretty cool huh?

What’s different here?

Well, I added in ‘…’ to the definition, and assigned groupvars using quos(…)
Prior to that I’d taken the first letter of the key column as a new additional grouping column.
So now we have 2 columns to facet_wrap.

Normally we’d use


Or vice versa.
But, I didn’t need to do that, I just specified ‘groupvars’ as the faceting variable, and changed the number of columns to prove it actually does what I want.

facet_wrap(groupvars, ncol = 2)

Cleverer people than me will be able to explain this magic, but in the meantime, if you need to create a faceted ggplot2 function, I hope this post and the previous one help you get off the ground.

If you like this, please consider liking it (wherever is appropriate) and / or sharing it.
Tag me on Twitter if you do ! @_johnmackintosh

Also clever peeps are welcome to explain the magic in the comments down below.

Cheers 🙂

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