Making plot functions with ggplot and aes_string

Question

In Hadley Wickham's ggplot2 book in chapter 10.3, he alludes to making plot functions. I want to make many similar plots that use faceting, but I cannot refer to a column. If all my references are in aesthetics then I can use aes_string and everything works. Facet_wrap seems not to have an analogue.

library(ggplot2)
data(iris)

This is the plot I want to functionalize.

pl.flower1 <- ggplot(data=iris, 
                    aes_string(x='Sepal.Length', y='Sepal.Width', color='Petal.Length')) +
                                 geom_point() +facet_wrap(~Species)

This works if I do not facet.

flowerPlot <- function(dat, sl, sw, pl, sp){
  ggplot(data=dat, aes_string(x=sl, y=sw, color=pl)) + geom_point()
}
pl.flower2 <- flowerPlot(iris, sl='Sepal.Length', sw='Sepal.Width', pl='Petal.Length')

What should "sp" be two lines below? A formula, a string? Maybe the whole aproach is wrong.

flowerPlotWrap <- function(dat, sl, sw, pl, sp){
      ggplot(data=dat, aes_string(x=sl, y=sw, color=pl)) + geom_point() +facet_wrap(sp)
    }
    pl.flower3 <- flowerPlotWrap(iris, sl='Sepal.Length', sw='Sepal.Width', pl='Petal.Length', sp= ?????)

In addition to an answer I would love pointer on how anyone approaches this problem?

As for how to approach solving this question, I'd probably check on [StackOverflow](http://stackoverflow.com/questions/8043247/writing-r-functions-with-optional-arguments) first. :) — joran, Apr 04 '12 at 04:28
Also asked here: http://stackoverflow.com/questions/11028353/passing-string-variable-facet-wrap-in-ggplot-using-r — Paul Lemmens, Jan 14 '14 at 11:49

score 22 · Accepted Answer · answered Apr 04 '12 at 04:29

facet_wrap expects a formula as its first argument, so I'd just coerce it with as.formula, and feed in my sp as a string:

flowerPlotWrap <- function(dat, sl, sw, pl, sp){
      ggplot(data=dat, aes_string(x=sl, y=sw, color=pl)) + 
      geom_point() +facet_wrap(as.formula(sp)) # note the as.formula
}
pl.flower3 <- flowerPlotWrap(iris, sl='Sepal.Length', 
                             sw='Sepal.Width', pl='Petal.Length', 
                             sp= '~Species')

Alternatively if my formula was always going to look like ~[columnname], I could just build that in to flowerPlotWrap and pass in the column name:

flowerPlotWrap <- function(dat, sl, sw, pl, sp){
      ggplot(data=dat, aes_string(x=sl, y=sw, color=pl)) + 
      geom_point() +facet_wrap(as.formula(sprintf('~%s',sp)))
}
pl.flower3 <- flowerPlotWrap(iris, sl='Sepal.Length', 
                             sw='Sepal.Width', pl='Petal.Length', 
                             sp= 'Species')

(kudos to the reproducible example in your question! If everyone asked questions as well as that they'd get answers much quicker).

Thanks for the clear answer. How did you figure out that facet_wrap expects a formula? — Ed Fine, Apr 04 '12 at 16:40
If you look at `?facet_wrap` it says `facet_wrap(facets,...)` and `facets: formula specifying variabls to facet by`. — mathematical.coffee, Apr 04 '12 at 23:34

score 5 · Answer 2 · answered Nov 06 '18 at 09:42

Here are some alternatives using new features from ggplot2 V3.0.0

Using strings :

flowerPlot <- function(dat, sl, sw, pl, sp){
  ggplot(data=dat, aes(x=!!ensym(sl), y=!!ensym(sw), color=!!ensym(pl))) + 
    geom_point() +
    facet_wrap(eval(expr(~!!ensym(sp))))
}

flowerPlot(iris, sl='Sepal.Length', sw='Sepal.Width', pl='Petal.Length', sp = 'Species')

Using names :

flowerPlot2 <- function(dat, sl, sw, pl, sp){
  ggplot(data=dat, aes(x=!!enquo(sl), y=!!enquo(sw), color=!!enquo(pl))) + 
    geom_point() +
    facet_wrap(eval(expr(~!!enquo(sp))))
}

flowerPlot2(iris, sl= Sepal.Length, sw=Sepal.Width, pl=Petal.Length, sp = Species)

score 1 · Answer 3 · answered Apr 04 '12 at 04:28

1

Your function worked fine for me unmodified if I just used sp='Species', i.e. the name of the variable you want to facet by.

flowerPlotWrap(iris, sl='Sepal.Length', sw='Sepal.Width', pl='Petal.Length', sp='Species')

enter image description here

answered Apr 04 '12 at 04:28

Marius

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Making plot functions with ggplot and aes_string

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