R中na.rm和na.omit的差异 [英] The difference of na.rm and na.omit in R

问题描述

我刚开始使用R并执行了以下语句:

I've just started with R and I've executed these statements:

library(datasets)
head(airquality)
s <- split(airquality,airquality$Month)
sapply(s, function(x) {colMeans(x[,c("Ozone", "Solar.R", "Wind")], na.rm = TRUE)})
lapply(s, function(x) {colMeans(na.omit(x[,c("Ozone", "Solar.R", "Wind")])) }) 

对于sapply，它返回以下内容:

For the sapply, it returns the following:

             5         6          7          8         9
Ozone    23.61538  29.44444  59.115385  59.961538  31.44828
Solar.R 181.29630 190.16667 216.483871 171.857143 167.43333
Wind     11.62258  10.26667   8.941935   8.793548  10.18000

对于lapply，它返回以下内容:

And for lapply, it returns the following:

$`5`
    Ozone   Solar.R      Wind 
 24.12500 182.04167  11.50417 

$`6`
    Ozone   Solar.R      Wind 
 29.44444 184.22222  12.17778 

$`7`
     Ozone    Solar.R       Wind 
 59.115385 216.423077   8.523077 

$`8`
    Ozone   Solar.R      Wind 
 60.00000 173.08696   8.86087 

$`9`
    Ozone   Solar.R      Wind 
 31.44828 168.20690  10.07586 

现在，我的问题是，为什么返回的值相似但不相同? na.rm = TRUE和na.omit是否应该做完全相同的事情?忽略缺失的值，仅计算我们拥有的值的均值?在那种情况下，我应该在两个结果集中都没有相同的值吗?

Now, my question would be, why are the returned values similar, but not the same? Isn't na.rm = TRUE and na.omit supposed to be doing the exact same thing? Omit the missing values and calculate the mean only for the values that we have? And in that case, shouldn't I have had the same values in both result sets?

非常感谢您的投入！

推荐答案

它们不应给出相同的结果.考虑以下示例:

They are not supposed to give the same result. Consider this example:

exdf<-data.frame(a=c(1,NA,5),b=c(3,2,2))
#   a b
#1  1 3
#2 NA 2
#3  5 2
colMeans(exdf,na.rm=TRUE)
#       a        b 
#3.000000 2.333333
colMeans(na.omit(exdf))
#  a   b 
#3.0 2.5

这是为什么?在第一种情况下，列b的平均值是通过(3+2+2)/3计算的.在第二种情况下，第二行将全部删除 (也是b的值，该值不是NA，因此在第一种情况下考虑)，因此由na.omit删除，因此平均值仅为(3+2)/2.

Why is this? In the first case, the mean of column b is calculated through (3+2+2)/3. In the second case, the second row is removed in its entirety (also the value of b which is not-NA and therefore considered in the first case) by na.omit and so the b mean is just (3+2)/2.

这篇关于R中na.rm和na.omit的差异的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！