Question

我正在学习R，我向你保证我已经高低搜索了这个答案。这很简单，但出于某种原因，我无法理解我的生活！

我有一个包含一个数字向量和两个因子的数据框：

team.weight <- c(150,160,120,100) # player's weight
team.jersey <- factor(c("blue", "green", "blue", "blue")) # player's jersey color
team.sex <- factor(c("male", "female", "female", "male")) # player's sex
team <- data.frame(team.jersey, team.sex, team.weight)

我想显示一个表（我忘记它叫什么），它显示了所有玩家的平均权重，即两个因子表的每个级别组合的平均值（team.weight）。

我可以手动完成，但必须有更好的方法！

mean(team.weight[c(team.jersey[1],team.sex[1])])
mean(team.weight[c(team.jersey[1],team.sex[2])])
mean(team.weight[c(team.jersey[1],team.sex[3])])
mean(team.weight[c(team.jersey[1],team.sex[4])])

mean(team.weight[c(team.jersey[2],team.sex[1])])
mean(team.weight[c(team.jersey[2],team.sex[2])])
mean(team.weight[c(team.jersey[2],team.sex[3])])
mean(team.weight[c(team.jersey[2],team.sex[4])])

mean(team.weight[c(team.jersey[3],team.sex[1])])
mean(team.weight[c(team.jersey[3],team.sex[2])])
mean(team.weight[c(team.jersey[3],team.sex[3])])
mean(team.weight[c(team.jersey[3],team.sex[4])])

mean(team.weight[c(team.jersey[4],team.sex[1])])
mean(team.weight[c(team.jersey[4],team.sex[2])])
mean(team.weight[c(team.jersey[4],team.sex[3])])
mean(team.weight[c(team.jersey[4],team.sex[4])])

非常感谢任何帮助。我知道答案是愚蠢的，但我无法理解它是什么。

Answer 1

tapply(team.weight, list(team$team.jersey, team$team.sex), mean)
#       female male
# blue     120  125
# green    160   NA

Answer 2

以下是plyr示例：

> library(plyr)
> ddply(team,.(team.jersey,team.sex),summarize,avgWeight=mean(team.weight))
  team.jersey team.sex avgWeight
1        blue   female       120
2        blue     male       125
3       green   female       160

矢量表是指两个因素

2 个答案: