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Rstudioで日本語がプロットできない．.Rprofileというファイルを~/ 以下に作って，以下に記述．
Rstudioを再起動したら，出来た．．．
こちらのサイトの内容の丸写しです．ありがたやー

setHook(packageEvent("grDevices", "onLoad"),
    function(...){
        if(.Platform$OS.type == "windows")
            grDevices::windowsFonts(sans ="MS Gothic",
                                    serif="MS Mincho",
                                    mono ="FixedFont")
        if(capabilities("aqua"))
            grDevices::quartzFonts(
              sans =grDevices::quartzFont(
                c("Hiragino Kaku Gothic Pro W3",
                  "Hiragino Kaku Gothic Pro W6",
                  "Hiragino Kaku Gothic Pro W3",
                  "Hiragino Kaku Gothic Pro W6")),
              serif=grDevices::quartzFont(
                c("Hiragino Mincho Pro W3",
                  "Hiragino Mincho Pro W6",
                  "Hiragino Mincho Pro W3",
                  "Hiragino Mincho Pro W6")))
        if(capabilities("X11"))
            grDevices::X11.options(
                fonts=c("-kochi-gothic-%s-%s-*-*-%d-*-*-*-*-*-*-*",
                        "-adobe-symbol-medium-r-*-*-%d-*-*-*-*-*-*-*"))
        grDevices::pdf.options(family="Japan1GothicBBB")
        grDevices::ps.options(family="Japan1GothicBBB")
        }
)
attach(NULL, name = "JapanEnv")
assign("familyset_hook",
       function() {
            winfontdevs=c("windows","win.metafile",
                          "png","bmp","jpeg","tiff","RStudioGD")
            macfontdevs=c("quartz","quartz_off_screen","RStudioGD")
            devname=strsplit(names(dev.cur()),":")[[1L]][1]
            if ((.Platform$OS.type == "windows") &&
                (devname %in% winfontdevs))
                    par(family="sans")
            if (capabilities("aqua") &&
                devname %in% macfontdevs)
                    par(family="sans")
       },
       pos="JapanEnv")
setHook("plot.new", get("familyset_hook", pos="JapanEnv"))
setHook("persp", get("familyset_hook", pos="JapanEnv"))