Replacing missing values coded by "." in an R dataframe

Question

I have a dataframe with missing values coded by ".", and I want to recode the values as NA:

df <- data.frame("h"=c(1,1,"."))

I try the following:

df$h[df$h == "."] <- NA

But the NA appears as a <NA>, and I can't execute commands like mean(df$h,rm.na=TRUE)

Does anyone know what the problem is? When I recode numbers as NA there's no problem

Thanks!

Answer 1

Use the is.na function. No need to convert to factor, although the fact that you had character values did cause coercion of what you wanted to be numeric.

> df <- data.frame("h"=c(1,1,"."))
> is.na(df) <- df=="."
> df
     h
1    1
2    1
3 <NA>

I'm not sure why @TylerRinker deleted his response regarding using 'na.strings', since I thought it to be the correct answer.

Comment: Looking at this a year later I realized that a) the OP misunderstood how missing values were displayed when they are in factors or character vectors, and b) that the main problem was not an error in recoding to an R-missing-value, which the OP's code already correctly had done correctly, but was rather the misspelling error that @joran identified.