From: Brian Candler <b.candler@...>
Date: 2009-01-15T18:30:34+09:00
Subject: Re: undefined method `[]' for nil:NilClass - how to prevent?

Mmcolli00 Mom wrote:
> #Searches through a text file and, at one row at a time, counts how many
> occurrences of the value exist for the column. For instance, if word,
> 'bird' exists in column1 row1 then count how many birds exist for the
> whole column. Next..count the occurrences of bird in the column 2. If
> the numbers do not match then outputs "Value does not contain a match:"
> +Value.

--- Here's a simple version

count1 = Hash.new(0)   # word => count in col1
count2 = Hash.new(0)   # word => count in col2

File.open("temp.txt") do |src|
  src.each_line do |line|
    word1, word2 = line.chomp.split(",")
    count1[word1] += 1
    count2[word2] += 1
  end
end

words = (count1.keys + count2.keys).uniq
words.each do |word|
  if count1[word] != count2[word]
    puts "Value does not contain a match: #{word}"
  end
end

--- However you can remove some duplication by choice
--- of a suitable data structure: a single hash which maps
--- to an array giving the counts in col1 and col2

# word => [col1_count, col2_count]
counts = Hash.new { |h,k| h[k] = Array.new(2,0) }

File.open("temp.txt") do |src|
  src.each_line do |line|
    line.chomp.split(",").each_with_index do |word, i|
      counts[word][i] += 1
    end
  end
end
counts.each do |word, cols|
  if cols.uniq.size != 1
    puts "Word #{word.inspect} occurs different times: #{cols.inspect}"
  end
end
-- 
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