R help - Jan 2013 - How to use geom_line (from ggplot) with aesthetics in a function?

Hello,

I have been struggling with this for a while, tried a few things, but no
clean solution so far. Here is an example from the documentation for
geom_line:

=========================================# Summarise number of movie ratings by
year of movie
mry <- do.call(rbind, by(movies, round(movies$rating), function(df) {
  nums <- tapply(df$length, df$year, length)
  data.frame(rating=round(df$rating[1]), year = as.numeric(names(nums)),
number=as.vector(nums))
}))

p <- ggplot(mry, aes(x=year, y=number, group=rating))
p + geom_line()

# Add aesthetic mappings
p + geom_line(aes(size = rating))
p + geom_line(aes(colour = rating))
=========================================
Notice the last two lines, "size = rating" and "colour =
rating", this has
knowledge of the structure of the data frame. My goal is to write a generic
function, which takes a few vectors and a few strings (column names) as
arguments, builds the data frame and then produces a chart. Building the
data frame is easy, but how should this function look like in the geom_line
code? The only solution which I found is something along the lines:

for( ii in indicatorNames ) {
   gg = gg + geom_line( aes_string( x="DATE", y=ii, color=paste(
sep="",
"\"", ii, "\"" )     ), size=0.75 )
}

Where indicatorNames is the name of the columns and DATE is the first
column of the data frame. What I don't like, not to mention I understand
completely, is the color=paste( sep="", "\"", ii,
"\"" ) - is this the
right solution for this purpose? Am I missing something?

Thanks in advance,
Ivan

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