When using Macports R with RStudio, make sure to install the "R-framework" port which includes support for the quartz graphics device on Mac OS X. This is different than simply installing the R port which disables the quartz graphics device.
Installing the "R-framework" port is necessary for RStudio as the RStudio graphics device relies on quartz. For additional details on the implementation of the "R-framework" port, see their support ticket.
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