R语言学习笔记

coursera上面的R语言学习有个作业是这样的：给你个表格，问表格中Ozone这一列为空值（na）的个数

 将csv表格导入到data变量中后，再执行下面语句

x<-data[is.na(data$Ozone),]

将所有Ozone值为na的行导入到X中，再由nrow函数计算出来即可

What is the mean of the Ozone column in this dataset? Exclude missing values (coded as NA) from this calculation.

x<-data[!is.na(data$Ozone),]
mean(x$Ozone)

Extract the subset of rows of the data frame where Ozone values are above 31 and Temp values are above 90. What is the mean of Solar.R in this subset?

 y<-data[!is.na(data$Ozone)&data$Ozone>31&data$Temp>90,]
mean(y$Solar.R)