“missing value where TRUE/FALSE needed” Error in if statement in R [duplicate]

Answer 1

when DATA[i,2] is NA, the comparison is also NA:

NA != NA
#[1] NA

You need to use function is.na to test wether you have NA value:

!is.na(NA)
#[1] FALSE

Hence, you should change your line of code to:

if(!is.na(DATA[i,2]) & !is.na(DATA[i,3]))