r - One of the factor's levels is an empty string; how to replace it with non-missing value? -

data frame aebysoc contains 2 columns - factor soc character levels , integer count count:

> str(aebysoc) 'data.frame':   19 obs. of  2 variables:  $ soc  : factor w/ 19 levels "","blood , lymphatic system disorders",..: 1 2 3 4 5 6 7 8 9 10 ...  $ count: int  25 50 7 3 1 49 49 2 1 9 ... 

one of levels of soc empty character string:

> l = levels(aebysoc$soc) > l[1] [1] "" 

i want replace value of level non-empty string, say, "not specified". not work:

> library(plyr) > revalue(aebysoc$soc, c(""="not specified")) error: attempt use zero-length variable name 

neither this:

> aebysoc$soc[aebysoc$soc==""] = "not specified" warning message: in `[<-.factor`(`*tmp*`, aebysoc$soc == "", value = c(na, 2l, 3l,  :   invalid factor level, na generated 

what's right way implement this? appreciate input/comment.

levels(aebysoc$soc)[1] <- "not specified" 

created toy example:

df<- data.frame(a= c("", "a", "b"))  df #  #1   #2 #3 b  levels(df$a) #[1] ""  "a" "b"  levels(df$a)[1] <- "not specified"  levels(df$a) #[1] "not specified" "a"             "b"  

edit

as per op's comments if need find according value in such case, can try

levels(aebysoc$soc)[levels(aebysoc$soc) == ""] <- "not specified"