R语言：给数据帧中某列长度小于4的值，全部在前面以0补齐
1.生成数据帧data

data <- data.frame(
    gender = c("Male", "Male","Female"), 
    height = c(152, 171.5, 165), 
    weight = c(81,93, 78),
    SPEED =c(1242,38,2622)
  )

运行的结果为：

data

gender height weight SPEED
1 Male 152.0 81 1242
2 Male 171.5 93 38
3 Female 165.0 78 2622

2.自定义补齐函数

new.function <- function(x){
  while(nchar(x)<4){
    temp <- paste(0,x)
    x <- temp
    x <- gsub(" ","",x)
  }
  return(x)
}

3.执行补齐，并且替换原数据帧

data$SPEED <-lapply(data$SPEED,new.function)

data

最终运行

data
gender height weight SPEED
1 Male 152.0 81 1242
2 Male 171.5 93 0038
3 Female 165.0 78 2622

data$SPEED[which(nchar(data$SPEED)<4)] <-1000 #这个是把长度小于4的，全部替换为1000.在此记录一下