Gasoline Mileage Log

November 2, 2012

I keep a log of gasoline mileage on a 3-by-5 card in the glovebox of my car. Recent entries on the card look like this:

   Date    Mileage  Miles  Gals MPG
----------  ------  -----  ----  --
08/18/2012  107679  290.8  13.1  22
08/26/2012  107934  255.3  10.4  24
09/05/2012  108197  262.9  12.2  22
09/16/2012  108518  321.7  13.8  23
10/02/2012  108762  243.5  12.2  20
10/09/2012  109028  265.6  11.5  24
10/18/2012  109306  278.1  12.4  22
10/27/2012  109589  283.3  11.1  26

Your task is to read a file containing mileage and gallons, compute miles per gallon, and produce an output similar to that shown above. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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4 Responses to “Gasoline Mileage Log”

  1. [...] today’s Programming Praxis exercise, our goal is to calculate and show the gas mileage given an input file [...]

  2. My Haskell solution (see http://bonsaicode.wordpress.com/2012/11/02/programming-praxis-gasoline-mileage-log/ for a version with comments):

    import Text.Printf
    import Text.XFormat.Read
    
    line :: String -> (Float, Float)
    line s = (m,g) where Just (m,_,g) = readf (Float, Space, Float) s
    
    showLog :: [(Float, Float)] -> [String]
    showLog es = "Miles  Gals  Avg" : "------ ---- ----" : zipWith (\(m2,g) (m1,_) ->
        printf "%.0f %.1f %.1f" m2 g ((m2 - m1) / g)) (tail es) es
    
    main :: IO ()
    main = mapM_ putStrLn . showLog . map line . lines =<< readFile "input.txt"
    
  3. Paul said

    My Python solution.

    print "{0:s}".format("Miles   Gals   Avg\n-----   ----  ----")
    oldmiles = None
    for line in open("mileage.txt"):
        miles, gals = [float(e) for e in line.split()]
        if oldmiles:
            avg = (miles - oldmiles) / (gals)
            print "{0:6.0f}  {1:3.1f}  {2:3.1f}".format(miles, gals, avg)
        oldmiles = miles
    

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