Non-numbers #5
Description
Your article is extremely thorough. You touched on a few of these points below, but maybe there's something interesting here below. This is not really an "issue", more of a comment.
# Things that are not floating point numbers ---
# In theory:
NaN # Not A (floating point) Number. IEEE 754 standard.
NA # Placeholder for an unknown value. Invented by R. Logical.
NULL # Empty object (like an empty set). Nothing.
Inf # Infinity
-Inf # Negative infinity
# In practice:
# Any mental model of NA/NaN will fail you. Dante's Inferno.
length(NA) # 1 Something there, but we don't know what.
length(NaN) # 1 Something there, but not representable.
length(NULL) # 0 Nothing there.
sqrt(-1) # NaN. 'i' in mathematics, not defined in floating point.
# NaN is an NA, but NA is not an NaN
is.nan(NA) # FALSE
is.na (NaN) # TRUE
min(c()) # Inf
min(c(NA), na.rm=TRUE) # Inf
min(NaN) # NaN
max(c()) # -Inf
max(c(NA), na.rm=TRUE) # -Inf
max(NaN) # NaN
# https://en.wikipedia.org/wiki/Empty_sum
sum(NA) # NA
sum(NA, na.rm=TRUE) # 0 # Horrible
mean(NA) # NA
mean(NA, na.rm=TRUE) # NaN
var(NA) # NA
var(NA, na.rm=TRUE) # NA
# https://en.wikipedia.org/wiki/Empty_product
prod(NA) # NA
prod(NA, na.rm=TRUE) # 1 # Horrible
NA | TRUE # TRUE
NA & FALSE # FALSE
# https://en.wikipedia.org/wiki/Division_by_zero
0/0 # NaN
1/0 # Inf. Shouldn't it be NaN?!
Inf >= NA # NA. If NA is placeholder, this should be TRUE!
NA * 0 # NA. Because NA could be Inf, and Inf*0 is NaN. Right???
NA ^ 0 # 1
NaN ^ 0 # 1
NA %in% 1:3 # FALSE
match(NA, 1:3) # NA
matrix(nrow=2,ncol=2) # matrix initializes with NAs
vector(mode="numeric", length=2) # vector initializes with 0s
# NULL can be assigned to an object.
x <- NULL
x
# NULL assigned to list elements removes them.
x <- list(1,"a",TRUE)
x[[1]] <- NULL
x
# NULL assigned to data.frame columns removes them
x <- data.frame(a=1:2, b=3:4)
x
x$a <- NULL
x
# https://blog.revolutionanalytics.com/2016/07/understanding-na-in-r.html
https://stats.stackexchange.com/questions/5686/what-is-the-difference-between-nan-and-na