How to combine similar fields parsed from CSV using Ruby - ruby-on-rails

Question

I am parsing baseball statistics from a CSV file, and I need to account for players who played for multiple teams within a season. Currently my code looks like this:
require 'CSV'
CSV.foreach("Batting-07-12-resaved.csv",{:headers=>:first_row}) do |row|
if row[7].to_i != 0 && row[5] != 0 && row[1].to_i == 2009
avg = row[7].to_f / row[5].to_f
puts row[0] + ": " + avg.round(3).to_s[1..-1]
end
end
The CSV headers look like this, and a player is identified by a key that sort of looks like their name and may recur based on different teams they played for (here are a few of the lines, copied from formatted file):
playerID yearID league teamID G AB R H 2B 3B HR RBI SB CS
aardsda01 2012 AL NYA 1
aardsda01 2010 AL SEA 53 0 0 0 0 0 0 0 0 0
aardsda01 2009 AL SEA 73 0 0 0 0 0 0 0 0 0
aardsda01 2008 AL BOS 47 1 0 0 0 0 0 0 0 0
aardsda01 2007 AL CHA 25 0 0 0 0 0 0 0 0 0
abadfe01 2012 NL HOU 37 7 0 1 0 0 0 0 0 0
abadfe01 2011 NL HOU 28 0 0 0 0 0 0 0 0 0
abadfe01 2010 NL HOU 22 1 0 0 0 0 0 0 0 0
abercre01 2008 NL HOU 34 55 10 17 5 0 2 5 5 2
abercre01 2007 NL FLO 35 76 16 15 3 0 2 5 7 1
abreubo01 2012 AL LAA 8 24 1 5 3 0 0 5 0 0
abreubo01 2012 NL LAN 92 195 28 48 8 1 3 19 6 2
So, for example, the bottom two lines, Bobby Abreu played for two different teams in the 2012 season.
How could I combine the numbers from these two rows under the same playerId for the 2012 season to calculate his 2012 batting average?

Answer 1

You need to keep a data structure that holds data about each playerID as you iterate through the CSV data. Using a hash would be perfect. ruby-doc.org manual page
require 'CSV'
# Hashes are built into ruby. Using a hash literal
# is more idomatic than h = Hash.new() */
h = {}
CSV.foreach("Batting-07-12-resaved.csv",{:headers=>:first_row}) do |row|
if row[7].to_i != 0 && row[5].to_i != 0 && row[1].to_i == 2009
playerData = h[row[0]]
if (!playerData)
playerData = [row[0], row[7].to_f, row[5].to_f]
else
playerData = [row[0], row[7].to_f+playerData[1], row[5].to_f+playerData[2]]
end
h[row[0]]=playerData
end
end
h.each {|key, value|
puts "#{value[0]} is #{value[1]/value[2]}"
}