no implicit conversion of nil into String error - ruby

Question

I have a ruby script that will create two files by taking and merging values from another file.
#Resources
require 'rubygems'
require 'csv'
col_date = []
col_constant1 = []
col_constant2 = []
col_appYear = []
col_statsDesc = []
col_keyStats =[]
col_weeklyTotal=[]
weekly_total = []
fname = "finalStats.csv" #variable for capture file
finalStatsFile = File.open(fname, "w") #write to capture file
fname2 = "weeklyStats.csv"
weeklyStatsFile = File.open(fname2, "w")
CSV.foreach('compareData.csv', converters: :numeric) do |row|
weekly_total << row[0] - row[1]
weekly_total.each do |data|
data << weekly_total.shift
weeklyStatsFile.puts data
end
end
#retrieve stats from original document
CSV.foreach("autoCapture.csv") {|row| col_date << row[0]}
CSV.foreach("autoCapture.csv") {|row| col_constant1 << row[1]}
CSV.foreach("autoCapture.csv") {|row| col_appYear << row[2]}
CSV.foreach("autoCapture.csv") {|row| col_statsDesc << row[3]}
CSV.foreach("autoCapture.csv") {|row| col_constant2 << row[4]}
CSV.foreach("autoCapture.csv") {|row| col_keyStats << row[5]}
CSV.foreach("weeklyStats.csv") {|row| col_weeklyTotal << row[0]}
col_date.zip(col_constant1, col_appYear, col_statsDesc, col_constant2, col_keyStats, col_weeklyTotal).each do |col_date, col_constant1, col_appYear, col_statsDesc, col_constant2,
col_keyStats, col_weeklyTotal|
finalStatsFile.puts col_date+", "+col_constant1+", "+ col_appYear+", "+col_statsDesc+", "+col_constant2+", "+col_keyStats+", "+col_weeklyTotal
end
In one file I wish to subtract the values in row[1] from the values in row[0] to create a new 'weekly_total' value. I then output this array of values in a file called weeklyStats.csv. This will output a column of values fine.
However, I want to join these values with another set from another file (autoCapture.csv) and when I try to zip them as arrays so that they read across in corresponding rows I get the error:
weeklyStats_csv.rb:42:in `+': no implicit conversion of nil into String (TypeError)
from weeklyStats_csv.rb:42:in `block in <main>'
from weeklyStats_csv.rb:40:in `each'
from weeklyStats_csv.rb:40:in `<main>'
I gather this means that the array zip will not catch an exception if the one of the values is nil and therefore cannot convert to string. The problem is, I have tried converting weekly_total to string and array as I thought that it may be the problem (a mismatch of types) but I just dont where to go from here. Can anyone help?

Answer 1

One of (or more) values in string
finalStatsFile.puts col_date+", "+col_constant1+", "+ col_appYear+", "+col_statsDesc+", "+col_constant2+", "+col_keyStats+", "+col_weeklyTotal
became nil. To fix the output you should explicitly cast them to strings:
finalStatsFile.puts col_date.to_s + ", " +
col_constant1.to_s + ", " +
col_appYear.to_s + ", " +
col_statsDesc.to_s + ", " +
col_constant2.to_s + ", " +
col_keyStats.to_s + ", " +
col_weeklyTotal.to_s
BTW, the whole clause might be rewritten in more rubyish manner:
finalStatsFile.puts [ col_date,
col_constant1,
col_appYear,
col_statsDesc,
col_constant2,
col_keyStats,
col_weeklyTotal ].map(&:to_s).join(', ')