Kata Four: Data Munging

kata.rb

# Houston Ruby group solution for http://codekata.pragprog.com/2007/01/kata_four_data_.html

require 'rspec'

class CalculateSpread
  
  def for_file(filename)
    smallest_day, smallest_spread = nil, infinity
    File.readlines(filename).each do |line|
      next unless valid_line?(line)
      line_params = parse_line(line)
      day = line_params.fetch(:day)
      this_spread = line_params.fetch(:spread)
      if this_spread < smallest_spread
        smallest_day = day
        smallest_spread = this_spread
      end
    end
    smallest_day
  end

  def parse_line(line)
    raise ArgumentError.new "Invalid Line" unless valid_line?(line)
    day, max, min = line.split(" ")
    spread = max.to_i - min.to_i
    {:day => day.to_i, :max => max.to_i, :min => min.to_i, :spread => spread}
  end
  
  def valid_line?(line)
    line.strip[0].to_i > 0
  end
  
  def infinity
    1.0/0
  end

end

describe CalculateSpread do

  let(:line_1) { "   1  88    59    74          53.8       0.00 F       280  9.6 270  17  1.6  93 23 1004.5"}
  let(:invalid_line) {"  mo  82.9  60.5  71.7    16  58.8       0.00              6.9          5.3" }
  
  context "#parse_line" do
    let(:parsed_results) { subject.parse_line(line_1) }
    it "should calculate a spread given a valid line" do
      parsed_results.fetch(:spread).should eq(29)
    end
    
    it "should return the max from a line" do
      parsed_results.fetch(:max).should eq(88)
    end

    it "should return the min from a line" do
      parsed_results.fetch(:min).should eq(59)
    end
    
    it "should return the day from a line" do
      parsed_results.fetch(:day).should eq(1)
    end
  
  end

  it "should know that a line is invalid" do
    subject.valid_line?(invalid_line).should be_false
  end
  
  it "should know that a line is valid" do
    subject.valid_line?(line_1).should be_true
  end
  
  it "should raise error if invalid line" do
    lambda{
      subject.spread_for_line(invalid_line)
    }.should raise_error
  end

end

weather.dat

(Unofficial, Preliminary Data). Source: <a
href="http://www.erh.noaa.gov/er/box/dailystns.html">www.erh.noaa.gov/er/box/dailystns.html</a>

<pre>
 MMU June 2002

  Dy MxT   MnT   AvT   HDDay  AvDP 1HrP TPcpn WxType PDir AvSp Dir MxS SkyC MxR MnR AvSLP

   1  88    59    74          53.8       0.00 F       280  9.6 270  17  1.6  93 23 1004.5
   2  79    63    71          46.5       0.00         330  8.7 340  23  3.3  70 28 1004.5
   3  77    55    66          39.6       0.00         350  5.0 350   9  2.8  59 24 1016.8
   4  77    59    68          51.1       0.00         110  9.1 130  12  8.6  62 40 1021.1
   5  90    66    78          68.3       0.00 TFH     220  8.3 260  12  6.9  84 55 1014.4
   6  81    61    71          63.7       0.00 RFH     030  6.2 030  13  9.7  93 60 1012.7
   7  73    57    65          53.0       0.00 RF      050  9.5 050  17  5.3  90 48 1021.8
   8  75    54    65          50.0       0.00 FH      160  4.2 150  10  2.6  93 41 1026.3
   9  86    32*   59       6  61.5       0.00         240  7.6 220  12  6.0  78 46 1018.6
  10  84    64    74          57.5       0.00 F       210  6.6 050   9  3.4  84 40 1019.0
  11  91    59    75          66.3       0.00 H       250  7.1 230  12  2.5  93 45 1012.6
  12  88    73    81          68.7       0.00 RTH     250  8.1 270  21  7.9  94 51 1007.0
  13  70    59    65          55.0       0.00 H       150  3.0 150   8 10.0  83 59 1012.6
  14  61    59    60       5  55.9       0.00 RF      060  6.7 080   9 10.0  93 87 1008.6
  15  64    55    60       5  54.9       0.00 F       040  4.3 200   7  9.6  96 70 1006.1
  16  79    59    69          56.7       0.00 F       250  7.6 240  21  7.8  87 44 1007.0
  17  81    57    69          51.7       0.00 T       260  9.1 270  29* 5.2  90 34 1012.5
  18  82    52    67          52.6       0.00         230  4.0 190  12  5.0  93 34 1021.3
  19  81    61    71          58.9       0.00 H       250  5.2 230  12  5.3  87 44 1028.5
  20  84    57    71          58.9       0.00 FH      150  6.3 160  13  3.6  90 43 1032.5
  21  86    59    73          57.7       0.00 F       240  6.1 250  12  1.0  87 35 1030.7
  22  90    64    77          61.1       0.00 H       250  6.4 230   9  0.2  78 38 1026.4
  23  90    68    79          63.1       0.00 H       240  8.3 230  12  0.2  68 42 1021.3
  24  90    88    84          67.5       0.00 H       350  8.5 010  14  6.9  74 48 1018.2
  25  90    72    81          61.3       0.00         190  4.9 230   9  5.6  81 29 1019.6
  26  97*   64    81          70.4       0.00 H       050  5.1 200  12  4.0 107 45 1014.9
  27  91    72    82          69.7       0.00 RTH     250 12.1 230  17  7.1  90 47 1009.0
  28  84    68    76          65.6       0.00 RTFH    280  7.6 340  16  7.0 100 51 1011.0
  29  88    66    77          59.7       0.00         040  5.4 020   9  5.3  84 33 1020.6
  30  90    45    68          63.6       0.00 H       240  6.0 220  17  4.8 200 41 1022.7
  mo  82.9  60.5  71.7    16  58.8       0.00              6.9          5.3
</pre>