Both vector query's can select the values from the data.frame as written,
however in the first form assigning a value to said selected numbers fails.
 Can you explain the reason this fails?

dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10))

dat$Value[dat$Value == "NA"] <- 1 #Why does this  fails to work,
dat$Value[dat$Value %in% NA] <- 1 #While this does work?


#Particularly when str() results in an equivalent class
dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10))
str(dat$Value[dat$Value %in% NA])
str(dat$Value[dat$Value == "NA"])

Thanks
Pat


-- 
Patrick Schmitz
Graduate Student
Plant Biology
1206 West Gregory Drive
RM 1500

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