我想回答的是

1. if(TEST) TRUE else FALSE允许TRUE与FALSE响应采用任何类或形式（与if_else()不同）.如果TEST是与ifelse()或if_else不同的向量，则该方法不起作用

• ifelse(TEST, TRUE, FALSE)是1）的矢量化版本。如有必要，它将回收TRUE和FALSE值。当我想返回一个向量时，我经常会遇到这个问题，在这种情况下，你需要使用一个列表，例如。
• 命令ifelse(c(TRUE, FALSE), list(c("TRUE1a", "TRUE1b"), c("TRUE2a", "TRUE2b")), list(c("FALSE1a", "FALSE1b"), c("FALSE2a", "FALSE2b"))
• 将返回list(c("TRUE1a", "TRUE1b"), c("FALSE2a", "FALSE2b"))
• if_else()要求返回值的类型相同，并且只有返回值的长度为1时才进行回收。

例病例

案例1：if（）为真，否则为假

这是baseR的一部分。它的行为受到以下事实的限制：if（）仅适用于标量（即长度（）== 1的向量）。与if_else（）不同，它不检查返回值是否属于同一类型

## These both work
if(is.na(NA)) TRUE else FALSE
if(is.na(NA)) TRUE else "FALSE"

## if() TRUE else FALSE will does not work if the test has a length() > 1 
##
## None of these work
if(is.na(c(NA, 1))) TRUE else  FALSE
if(is.na(NA, 1)) TRUE else c(FALSE, FALSE)
if(is.na(c(NA, 1))) c(TRUE, TRUE) else c(TRUE, FALSE)

## However, if the test value has length() == 1, but return values
## have a length() > 1 it will still work.
## It just returns the appropriate value which happens to be a vector
## This behavior is consistent with this approach not checking that the return values are of the same type or length
if(is.na(NA)) c(TRUE, TRUE) else c(FALSE)
if(is.na(1)) c(TRUE, TRUE) else c(FALSE)

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第二种情况：ifelse（）
这是if（）TRUE else FALSE和base函数的矢量化版本。类似于标量版本，因为它不确保返回值的类型相同

## These both work
ifelse(is.na(NA), TRUE, FALSE)
## This works here, but doesn't work with `if_else`
ifelse(is.na(NA), TRUE, "FALSE")

## ifelse() will *work* (i.e. not throw an error) if the length of the return values
## is longer than the test vector. However, it has unexpected behavior in that
## it only returns the first value of the relevant vector. This is because the
## test value is only of length 1.
##
## These works but only returns the first element of the return values
## if() TRUE else FALSE would return the entire return value (i.e. a vector)
## if_else() would throw an error.
ifelse(is.na(NA), c(TRUE, TRUE, TRUE), FALSE)
ifelse(is.na(NA), c(TRUE, TRUE, TRUE), c(FALSE, FALSE))

## Unexpectedly (to me anyway) if for every element in the test vector there is
## a corresponding element return vector, it will return that element. I can see
## how this is consistent with R's default recycling behavior
##
## This works and returns the first and second elements of the TRUE vector
ifelse(is.na(c(NA, NA)), c(TRUE, NA), FALSE)

## This works and recycles the TRUE vector
ifelse(is.na(c(NA, 1)), TRUE, FALSE)
## This works as is a more complex illustration of recycling
ifelse(is.na(c(NA, NA, NA, NA)), c(TRUE, NA), FALSE)

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案例3：if_else（）

此tidyverse函数要求两个返回变量的类型相同。这就是为什么它在错误消息中显示“无法合并...”

## This works
if_else(is.na(NA), TRUE, FALSE)
## This doesn't
if_else(is.na(NA), TRUE, "FALSE")

## if_else() will recycle the TRUE and FALSE values based on the size of the TEST value
## However, it will only recycle the return values if it is of length 1.  As a result, it won't work if the length of either return values is > 1, but < length(TEST).
##
## This works
if_else(is.na(c(NA, 1)), TRUE, FALSE)
## This does too, the TRUE case is recycled
if_else(is.na(c(NA, NA)), TRUE, c(FALSE, FALSE))
## This doesn't work since the TRUE cases is longer than the test cases
if_else(is.na(c(NA, 1)), c(TRUE, TRUE, TRUE), FALSE)

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