On Monday 11 October 2010 16:56:58, Lorenzo Isella wrote:
Dear All, Another I/O question. Let us say that you are given a list of files file1.dat, file2.dat...file10.dat and so on (i.e. every file is indexed by a number and every file is a single column where every entry is a string without spaces). In the snippet below I read file1.dat, convert it to a list and then print out its length. Now, how can I iterate the process on file1.dat, file2.dat and file3.dat and store the lengths in a list?
fileLength :: FilePath -> IO Int fileLength file = fmap length (readFile file) filename :: Int -> FilePath filename i = "file" ++ show i ++ ".dat" getAllLengths :: [Int] -> IO [Int] getAllLengths nums = mapM (fileLength . filename) nums If you want something other than the character count, instead of fileLength use e.g. countLines :: FilePath -> IO Int countLines file = fmap (length . lines) (readFile file) or whatever you're interested in. Another nice thing is often forM (from Control.Monad) forM nums $ \i -> do let filename = "file" ++ show i ++ ".dat" contents <- readFile filename let result = function contents doSomethingOrNot return result
I would like to map the file reading and following operations on the list [1,2.3], but that is giving me a headache. It is relatively easy to create the file name
filename="file"++(show i)++".dat" , for i=1,2,3
but it the the iteration part that is giving me troubles. Any suggestion is appreciated. Cheers
Lorenzo