标签： r
mean(data$NumKilled if data$ForAffil = TRUE, na.rm = TRUE)
此命令不起作用-有没有办法将其更改为命令data$NumKilled或data$ForAffil = TRUE时R运行data$ForAffil = Yes的平均值？
data$NumKilled
data$ForAffil = TRUE
data$ForAffil = Yes