# [R] use ggplot in a function to which a column name is given

jiho jo.irisson at gmail.com
Thu Dec 13 10:45:32 CET 2007

```Hi everyone, Hi ggplot users in particular,

ggplot makes it very easy to plot things given their names when you
use it interactively (and therefore can provide the names of the
columns).
qplot(x,foo,data=A) where A has columns (x,y,foo,bar) for example

but I would like to use this from inside a function to which the name
of the column is given. I cannot find an elegant way to make this
work. Here are my attempts:

#------------------------------------------------------------

library(ggplot2)

A = data.frame(x=rep(1:10,10), y=rep(1:10,each=10), u=runif(100),
v=rnorm(100))

# goal: extract values for y<=5 and plot them, either for u or v

foo1 <- function(uv="u")
{
# solution 1: do not use the data argument at all
# 	(forces the use of qplot, could be more elegant)
B = A[A\$y<=5,]
qplot(B\$x, B\$y, fill=B[[uv]], geom="tile")
}

foo2 <- function(uv="u")
{
# solution 2: extract and rename the colums, then use the data argument
# 	(enables ggplot but could be shorter)
B = A[A\$y<=5,c("x","y",uv)]
names(B)[3] = "value"
# rem: cannot use rename since rename(B,c(uv="value")) would not work
qplot(x, y, fill=value, data=B, geom="tile")
# or
# ggplot(B,aes(x=x,y=y,fill=value)) + geom_tile()
}

foo3 <- function(uv="u")
{
# solution 3: use the data argument and perform the extraction
directly in it
#	(elegant and powerful but can't make it work)
ggplot(A[A\$y<=5,c("x","y",uv)],aes(x=x,y=y,fill=???)) + geom_tile()
# or
ggplot(A[A\$y<=5,],aes(x=x,y=y,fill=???)) + geom_tile()
# or ...
}

print(foo1("u"))
print(foo1("v"))
print(foo2("u"))
print(foo3("u"))

#------------------------------------------------------------

Any help in making foo3 work would be appreciated. Thanks in advance