r - is.nan() 行为

Question

创建了一个数据框:

simpleDF<- structure(list(vals = c(NA, NaN, 2)), .Names = "vals", row.names = c(NA, 
-3L), class = "data.frame")


> is.na(simpleDF$vals)
[1]  TRUE  TRUE FALSE
> is.nan(simpleDF$vals)
[1] FALSE  TRUE FALSE

现在，当我更改数据框以包含字符串值时:

simpleDF <- structure(list(vals = structure(c(NA, 2L, 1L, 3L), .Label = c("2", 
"NaN", "test"), class = "factor")), .Names = "vals", row.names = c(NA, 
-4L), class = "data.frame")

> is.na(simpleDF$vals)
[1]  TRUE FALSE FALSE FALSE
> is.nan(simpleDF$vals)
[1] FALSE FALSE FALSE FALSE

我不明白为什么 NaN 不再被 is.nan() 识别？当然会有一个解释..

Answer 1

NaN 是一个仅在数字向量中有意义的值，因此当它所在的向量类是(显式或隐式)从数字转换为字符或因子。

vals
# [1]  NA NaN   2
as.character(vals)
# [1] NA    "NaN" "2" 
c(vals, "A")
# [1] NA    "NaN" "2"   "A"