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?

Answer 1

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).

Answer 2

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)