Handling NA values
On Feb 16, 2013, at 11:55 AM, Christofer Bogaso <bogaso.christofer at gmail.com> wrote:
Hello again, I have a question on who sum() handle the NA values.
sum(c(NA, 1), na.rm = TRUE)
[1] 1 I understand this. However could not agree with following:
sum(c(NA, NA), na.rm = TRUE)
[1] 0 Where this '0' is coming from? Should not it be NA itself? Thanks and regards,
The result of: sum(c(NA, NA), na.rm = TRUE) is to sum an empty set, hence the 0.
na.omit(c(NA, NA))
logical(0) attr(,"na.action") [1] 1 2 attr(,"class") [1] "omit"
sum(logical(0))
[1] 0 If you retained the NA's, then the result is undefined:
sum(c(NA, NA))
[1] NA See: http://rwiki.sciviews.org/doku.php?id=tips:surprises:emptysetfuncs for more information. Regards, Marc Schwartz