R - Convert a column of factors into binary characters without loss of information -

i new r , teaching myself how use it. i'm using r version 3.0.1 on windows 7 (if that's relevant).

i have trouble converting data of factors characters. data follows:

activity <- c("1","2","10","zz") 

what want have output

activity <- c("01","02","10","zz")  

where, each string, if contains 1 character, should prefixed 0 (as shown above).

i tried using "as.character" doesn't add 0 before. found sprintf , tried:

activity <- sprintf("%02d", (activity)) # [1] "01" "02" "03" "04" 

this adds 0 "0" in front of single data found what's troublesome modifies levels of data (as shown above).

does know what's wrong here , how can fix it? thank you.

you can use regular expressions, particularly function sub replace single digit 0 followed digit. should replace levels of factor activity whole data changed accordingly:

levels(activity) <- sub("^([0-9])$", "0\\1", levels(activity)) # [1] 01 02 10 zz # levels: 01 02 10 zz 

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edit: if want not replace numbers string 1 character, can replace [0-9] .. is:

# suppose x is: x <- c("1", "a", "y", "!", "bb", "45")  x <- factor(x, levels=unique(x))  levels(x) <- sub("^(.)$", "0\\1", levels(x)) # [1] 01 0a 0y 0! bb 45 # levels: 01 0a 0y 0! bb 45