df$freq <- as.factor(df$freq)

df$time <- as.factor(df$time)

我学会了如何使用循环绘制一个因子级别的直方图：

windows(width=19, height=10)

par(las=1, cex.lab=0.75, cex.axis=0.6, bty="n", mgp=c(1, 0.6, 0),

oma=c(2, 4, 2, 0) + 0.1, mar=c(4, 0, 3, 3) + 0.1)

a <- layout(matrix(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,

18, 19, 20, 21), nrow=3, ncol=7, byrow=T))

layout.show(a)

for (i in 1:length(unique(df$freq))) {

value <- subset(df, freq == unique (df$freq)[i])

hist(value$thr, main=paste0("freq: ", unique(df$freq)[i]))

}

我为两个因素尝试了这个循环的变体，但遗憾的是这不起作用：

for (i in 1:length(unique(df[c("freq", "time")]))) {

value <- subset(df, freq == unique (df$freq)[i] & time == unique(df$time)[i])

hist(value$thr, main=paste0("freq: ", unique(df$freq)[i]))

}

我还想学习如何根据两个因素（不仅仅是一个）的水平标记每个直方图......