if语句中的逻辑(0) [英] logical(0) in if statement

问题描述

此行:

which(!is.na(c(NA,NA,NA))) == 0

产生logical(0)

此行

if(which(!is.na(c(NA,NA,NA))) == 0){print('TRUE')}

生成:

Error in if (which(!is.na(c(NA, NA, NA))) == 0) { : 
  argument is of length zero

为什么有错误?什么是逻辑(0)

Why there is an error? What is logical(0)

推荐答案

logical(0)是长度为0的逻辑基本类型的向量.之所以得到这个，是因为您问这个向量的哪些元素等于0:

logical(0) is a vector of base type logical with 0 length. You're getting this because your asking which elements of this vector equal 0:

> !is.na(c(NA, NA, NA))
[1] FALSE FALSE FALSE
> which(!is.na(c(NA, NA, NA))) == 0
logical(0)

在下一行中，您要询问零长度向量logical(0)是否等于0，但不是.因为无法将长度为0的向量与标量进行比较，所以会出现错误.

In the next line, you're asking if that zero length vector logical(0) is equal to 0, which it isn't. You're getting an error because you can't compare a vector of 0 length with a scalar.

您可以检查第一个向量的长度是否为0:

Instead you could check whether the length of that first vector is 0:

if(length(which(!is.na(c(NA,NA,NA)))) == 0){print('TRUE')}

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