Quelque-chose comme suit ? set.seed(20200312)dfecm <- data.frame( rat = paste("R", 1:100, sep =""), zone = rep(c(1,2), 50), val1 = rnorm(100), val2 = rnorm(100), stringsAsFactors = FALSE) library(dplyr) dfecm %>% mutate(rat = sprintf("R%03d", as.numeric(gsub("^R", "", rat)))) %>% arrang...