na.rm 缺失值处理(na. RM missing value processing)

is.na 检测缺失值，返回结果为true,false

na.rm=TRUE 很多函数有这个参数，即在计算之前移除缺失值，并使用剩余值计算。

https://www.cnblogs.com/GhostBear/p/8416897.html

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is. Na detects the missing value, and the returned results are true and false

na. RM = true many functions have this parameter, that is, remove the missing value before calculation and use the residual value for calculation.

https://www.cnblogs.com/GhostBear/p/8416897.html