从数据集创建多个直方图以显示在同一面板中

Question

我想创建多个直方图，如下图所示

这是数据集： https://drive.google.com/file/d/0B4Mldbnr1-avLUg1REJRRzFUZU0/view?usp=sharing

这是我到目前为止所做的代码，但是回来了错误：

source("load_data.R")
#library(lattice)
load_data <- function() {
  data <- "E:/Intro Data Science/ClassActivity/Lab Session 5&6/dataset.txt"
  data <- read.table(data, header=TRUE, sep=";", colClasses=c("numeric", "numeric", "numeric", "numeric", "numeric", "numeric", "numeric", "numeric"))
}
  par(mfrow = c(3,1), mar=c(4, 4, 3,1))

  hist (subset(data, globalActivePower==0)$SubMetering2, col = "red") 
  hist (subset(data, globalActivePower==1)$SubMetering2, col = "red")
  hist (subset(data, globalActivePower==2)$SubMetering2, col = "red")

错误消息是

Error in hist.default(subset(data, globalActivePower == 0)$SubMetering2,  : 
  'x' must be numeric

提前致谢 感谢你的帮助，欢呼声