R 特定命令的进度行

有这样的代码：

df <- data.frame(text = c("I love to travel to London",
                          "Germany was a fun country to visit."), stringAsFactors = FALSE)

replace_cities_countries <- function(string, replacement) {
  library(maps)
  data(world.cities)
  patterns <- unique(c(world.cities$name, world.cities$country.etc))
  for (i in seq_along(patterns))
    string <- gsub(patterns[i], replacement, string, perl=TRUE)
  string
}

sapply(df$text, replace_cities_countries, replacement='HOORAY!')

df可能使用

df <- data.frame(text = c("I love to travel to London",
                          "Germany was a fun country to visit."), stringsAsFactors = FALSE)

counter <- 0
max_count <- length(df$text)

my_function <- function(x) {
  counter <<- counter + 1  # Note the double <<
  cat("Iter", counter, "/", max_count, "\n")
  return(nchar(x))
}

> out <- sapply(df$text, my_function)                                                                
Iter 1 / 2                                                                                           
Iter 2 / 2

> out                                                                                                
         I love to travel to London Germany was a fun country to visit.                              
                                 26                                  35

> length(out)                                                                                        
 [1] 2