R help - Dec 2007 - use ggplot in a function to which a column name is given

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  
for your expertise.

JiHO
---
http://jo.irisson.free.fr/

Follow up.

On 2007-December-13  , at 10:45 , jiho wrote:
> 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")
> }
---> actually this does not even work currently:
	Error in eval(expr, envir, enclos) : object "B" not found
Which only leaves the most inelegant solution: 2

JiHO
---
http://jo.irisson.free.fr/

Hi Jiho,

The key to solving this problem is to use aes_string instead of aes.
Instead of the complicated munging that aes does to get the names of
the variables, aes_string works directly with strings, so that:

aes_string(x = "mpg", y = "wt") == aes(x = mpg, y = wt)

So your function would look like:

foo4 <- function(uv="u") {
  ggplot(A, aes_string(x = "x", y= "y", fill = uv)) +
geom_tile()
}

Or

ggplot(A, aes(x=x, y=y)) + aes_string(fill=uv) + geom_tile()

Hope that helps!  (And I've made a note to better document aes_string
so you can discover after looking at aes)

Hadley

On 12/13/07, jiho <jo.irisson at gmail.com> wrote:
> 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
> for your expertise.
>
> JiHO
> ---
> http://jo.irisson.free.fr/
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
http://had.co.nz/