How to handle conditional data.frame subscripts that contain NAs?

Question

Is there a way to have conditional subscripts if the conditional vector contains NAs? Assume i have a data.frame like this

dframe <- data.frame(a=c(1,32,4,5,8),b=c(1,2,3,4,5),d=c(NA,5,5,10,9))
dframe[dframe$d > 9,"a"] <- NA

If it was not for the NA in dframe$d this would be straight forward. I have seen %in% syntax like here to get around NAs, but do not know how to manage it for conditions. I can see that this is somewhat of a general problem, since I am not quite sure whether I want to obtain an NA for the missing value in the condition or something else. But I am also interested to learn how people handle this situation.

In my specific situation in would simply be helpful when NA was treated like FALSE in the condition.

Answer 1

You can just restrict your indexing to the non NA values

dframe[ dframe$d > 9 & !is.na(dframe$d), "a"] <- NA

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Edit: Here is a more compact alternative from the R Inferno:

dframe[ which(dframe$d > 9), "a"] <- NA