Hi Romzero, This gets the job done, though it is not the most elegant solution ever (for those I'd take a look at the ggplot2 or lattice packages).
## Read in data la <- read.table(textConnection(" Days Weight 0 178.00 0 250.00 0 242.00 0 239.00 0 223.00 0 188.00 0 237.00 0 212.00 0 273.00 0 191.00 0 173.00 0 233.00 0 227.00 0 253.00 0 232.00 4 177.00 4 249.00 4 241.00 4 238.00 4 222.00 4 188.00 4 236.00 4 211.00 4 272.00 4 190.00 4 172.00 4 232.00 4 226.00 4 252.00 4 231.00"), header = TRUE) closeAllConnections() ## calculate mean by day tmp <- c(with(la, by(Weight, Days, mean))) ## your plot plot(Weight ~ Days, data = la) ## add in the daily means points(x = as.numeric(names(tmp)), y = tmp, col = "blue", cex = 2, pch = 16) Cheers, Josh On Sun, Nov 7, 2010 at 10:53 AM, romzero <romz...@yahoo.it> wrote: > > Hi, i need to draw a plot with means of values, reading a table from > datafile. > > Example of datafile: > > Days Weight > 0 178.00 > 0 250.00 > 0 242.00 > 0 239.00 > 0 223.00 > 0 188.00 > 0 237.00 > 0 212.00 > 0 273.00 > 0 191.00 > 0 173.00 > 0 233.00 > 0 227.00 > 0 253.00 > 0 232.00 > 4 177.00 > 4 249.00 > 4 241.00 > 4 238.00 > 4 222.00 > 4 188.00 > 4 236.00 > 4 211.00 > 4 272.00 > 4 190.00 > 4 172.00 > 4 232.00 > 4 226.00 > 4 252.00 > 4 231.00 > > if i use "plot(Weight~Days, data=la)" the result is this > http://r.789695.n4.nabble.com/file/n3031068/weightm.jpg > > how can i draw a plot with means for each days? > > tnx for help :) > > -- > View this message in context: > http://r.789695.n4.nabble.com/mean-on-a-plot-tp3031068p3031068.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles http://www.joshuawiley.com/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.