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What is the difference between NaN and Inf, and NULL and NA in R?

What is the difference between NaN and Inf, and NULL and NA in R?

Why ?NA and ?NULL tell me that "NA" has a length of "1" whereas NULL has a length of "0"?

Solution

  • In R language, there are two closely related null-like values: NA and NULL. Both are used to represent missing or undefined values.

    NULL represents the null object, it's a reserved word. NULL is perhaps returned by expressions and functions, so that values are undefined.

    NA is a logical constant of length 1, which contains a missing value indicator. NA can be freely coerced to any other vector type except raw. There are also constants NA_integer_, NA_real_, NA_complex_ and NA_character_ of the other atomic vector types which support missing values: all of these are reserved words in the R language.