r - Replacing NA's with asterisks (*) -

i have data set read .csv file. after editing work, need write .txt file (i) quotes removed (ii) every na in whole file replaced asterisk, *, , (iii) first row (variable names) excluded.

the following scripts, far, remove quotes , wondering how can (ii) , (iii) can added or may done.

write.table(ped5, "ped5.txt" ,row.names=false) ped5 <- read.table("ped5.txt", header=true) write.table(ped5, "ped7.txt", row.names=false, quote=false) 

any appreciated!

for (ii) use na = "*" , (iii) col.names=false.
so:

write.table(ped5,"ped7.txt",row.names=false,quote=false, na="*", col.names=false) 

it's find on help page write.table (?write.table).