If you follow the first alternative suggested by Gei and use
PerformanceAnalytics, the RF function (which is an alias for
makeReturnFrame) in my qmao
package<https://r-forge.r-project.org/R/?group_id=1113> can
assist you in merging the data.

library(qmao)
library(PerformanceAnalytics)
charts.PerformanceSummary(RF(getSymbols(c("QQQ","EWG","EWI"))))

The chart_Series function (note the underscore) can also handle multiple
time series

library(quantmod)
getSymbols(c("SPY","DIA"))

# This will put 2 price series on a chart
thm <- chart_theme()
thm$col$line.col <- 'lightblue'
chart_Series(Cl(SPY),theme=thm)
add_Series(Cl(DIA),on=1)

# although there seems to be a bug preventing you from changing the
color/theme of the second series you add
dev.new()
chart_Series(Cl(SPY))
add_Series(Cl(DIA),theme=thm,on=1)

Regards,
Garrett

On Mon, Sep 26, 2011 at 10:28 PM, Gei Lin <gmonaie@gmail.com> wrote:

> One alternative is to use PerformanceAnalytics.  use merge.xts to merge
> your
> two time series by their common indices and plot using
> charts.PerformanceSummary
>
> Another alternative is to use the package PApages on r-forge which allows
> you to compare time series returns versus a benchmark.
>
> On Mon, Sep 26, 2011 at 11:20 PM, Chris Waggoner <chris.is.fun@gmail.com
> >wrote:
>
> > I'd like to overlay two plots in quantmod. Use the wider time period only
> > for the axes. *(Or rather,* xmin= min(t1_min, t2_min); xmax= max(t1_max,
> > t2_max)*.)*
> >
> > This question was asked a little over two years ago and answered two
> > ways: 1<https://stat.ethz.ch/pipermail/r-sig-finance/2009q2/003982.html>
> > 2 <https://stat.ethz.ch/pipermail/r-sig-finance/2009q2/003985.html>. The
> > second answer requires editing quantmod internals (something I'm not
> > comfortable doing) and in any case Jeff Ryan may have improved quantmod
> in
> > the intervening period.
> >
> >
> > Jeff asked in his response *1* why anyone would want to overlay two time
> > series. In my case, I'm making a report for a client and I want to
> > juxtapose
> > the client's returns vis-à-vis the S&P. It would also be nice to be able
> to
> > plot 2-3 series on top of each other for visual study.
> >
> >
> > Cheers to all who volunteer help on this list.
> > -Chris Waggoner
> >
> >        [[alternative HTML version deleted]]
> >
> >
> > _______________________________________________
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> > -- Also note that this is not the r-help list where general R questions
> > should go.
> >
>
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