So I have a text full of x and y coordinates in the for x_y new line delimited. Here is the first 3 lines: 68_1 153_16099247764943158 153_775041589 I'm massaging the data to run a liner regression on it. At the moment the program I'm writing looks like this (still a work in progress...): module Main where import qualified Data.Text as T import qualified Data.Text.IO as TI import Numeric.GSL.Fitting.Linear import Data.Packed.Vector buildList :: IO [[T.Text]] buildList = TI.readFile "lin_reg_data.txt" >>= return . map (T.split (=='_')) . T.lines --main :: IO () --main = do -- values <- buildList -- let heads = fromList $ map (\x -> read (T.unpack . head $ x):: Double) values -- let lasts = fromList $ map (\x -> read (T.unpack . last $ x):: Double) values -- print linear heads lasts I'm just trying to find a way to not iterate over "vaues" twice as that seems like a waste of computing time to me. Of course any advice on this would be appreciated. Bryce On 01/28/2013 10:42 AM, Ozgur Akgun wrote:

Hi,

On 28 January 2013 18:37, Bryce Verdier mailto:bryceverdier@gmail.com> wrote:

I know I can do this with calling 2 maps on the container, but I would also like to do this in one iteration.

As a learning experience, may I suggest you post the code you would have written with two maps? Then we can try and improve on that to have only one map.

Best,

-- Ozgur Akgun

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Hi, What is the point of using Text here? You may rewrite buildList as follows (using <$> from Control.Applicative): buildList = transpose . map (T.split (=='_')) . T.lines <$> TI.readFile "lin_reg_data.txt" Regards Sylvain 2013/1/28 Bryce Verdier

On 01/28/2013 11:32 AM, Martin Drautzburg wrote:

...

On Monday, 28. January 2013 19:37:53 Bryce Verdier wrote:

...

Hi All,

At the moment I have a list of lists. The inner list is a coordinate, like (x,y) but is [x,y] instead. What I would like to do is group all the x's into one list, and the y's into another. I know I can do this with calling 2 maps on the container, but I would also like to do this in one iteration.

Something like this? groupMe = foldl (\[rx,ry] [x,y] -> [x:rx,y:ry]) [[],[]]

*Main> groupMe [[1,2],[1,3],[2,3]] [[2,1,1],[3,3,2]]

Thank you all for your responses. This is what I ultimately went with (pasted below). If anyone would like to share a way to improve this (because I know it can be), please share. I'm still learning. :)

module Main where

import qualified Data.Text as T import qualified Data.Text.IO as TI (readFile) import Data.List (transpose) import Numeric.GSL.Fitting.Linear (linear) import Data.Packed.Vector (fromList)

buildList :: IO [[T.Text]] buildList = TI.readFile "lin_reg_data.txt" >>= return . transpose . map (T.split (=='_')) . T.lines

main :: IO () main = do values <- buildList let values2 = map (fromList . map (\x -> read (T.unpack x):: Double)) values print [linear (head values2) (last values2)]

Warm regards, Bryce

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