I am new to R and would appreciate help in dealing with this problem. I worked on a some African grasses and have a matrix based on TukeyHSD test showing how the species differ from each other. A value of 1 means they DON't differ significantly from each other, whiles 0 means they differ significantly from each other. I want to assign letters to these combination and show them on a histogram. How to I go about this. I attach the file to the mail and look forward to hearing for you http://www.nabble.com/file/p24697164/R-request-Bright.xls R-request-Bright.xls . Bright -- View this message in context: http://www.nabble.com/Graphing-Significant-difference-tp24697164p24697164.html Sent from the R help mailing list archive at Nabble.com.