Ruby未定义方法`[]'表示nil：NilClass（NoMethodError）错误

Question

I'm trying to figure out why I keep getting the following error:

From the following code:

def information_transfer()
  file_contents = CSV.read("test.csv", col_sep: ",", encoding: "ISO8859-1")
  file_contents2 = CSV.read("applicantinfo.csv", col_sep: ",", encoding:"ISO8859-1")
  arraysize = file_contents.length
  arraysize1 = file_contents2.length
  for i in 1..arraysize
    for x in 1..arraysize1
      if file_contents[i][0] == file_contents2[x][0]
        CSV.open("language_output.csv", "wb") do |csv|
          csv << [file_contents[i][0], file_contents[i][1], file_contents[i][2],file_contents[i][3], file_contents[i][4], 
          file_contents[i][5], file_contents[i][6], file_contents[i][7], file_contents[i][8],file_contents[i][9], 
          file_contents[i][10], file_contents[i][11], file_contents[i][12], file_contents[i][13], file_contents[i][14],
          file_contents[i][15], file_contents[i][16], file_contents[i][17], file_contents[i][18], file_contents2[i][24],file_contents2[i][25], 
          file_contents2[i][26],file_contents2[i][27], file_contents2[i][28], file_contents2[i][29], file_contents2[i][30], file_contents2[i][31], file_contents2[i][32], file_contents2[i][33]]
        end
     end
   end
 end
end

I'm basically trying to take two individual .csv files and merge certain columns together. I have two arrays (file_contents and file_contents2) that are reading the individual csv files and storing the contents in arrays. For some reason i'm getting a syntax error for my if statement. I was hoping someone could help me figure out why the if statement that I wrote isn't valid. I figured it would be. Any help is appreciated. Thanks!

Answer 1

One of your arrays file_contents or file_contents2 might be empty. Output both, as well as printing file_contents[i][0] and file_contents2[x][0] before your if statement.

You can make a simple change that should work:

for i in 0..arraysize for x in 0..arraysize1

And add an error check:

if !file_contents[i].blank? and !file_contents2[x].blank? and file_contents[i][0] == file_contents2[x][0]

Answer 2

for i in 1..arraysize
  for x in 1..arraysize1

Array indexes run from 0 to length − 1 in Ruby; loop in 0...arraysize instead.

If file_contents2[i] can or should be written as file_contents2[x] , you can just loop over the arrays' contents directly:

for a in file_contents
  for b in file_contents2

and use slices to get consecutive array elements into another array:

def information_transfer()
  file_contents = CSV.read("test.csv", col_sep: ",", encoding: "ISO8859-1")
  file_contents2 = CSV.read("applicantinfo.csv", col_sep: ",", encoding: "ISO8859-1")
  for a in file_contents
    for b in file_contents2
      if a[0] == b[0]
        CSV.open("language_output.csv", "wb") do |csv|
          csv << a[0..18] + b[24..33]
        end
      end
    end
  end
end

and if you're trying to join the two files one-to-one, you can do that more efficiently by putting the key into a hash. You also probably didn't mean to reopen the output file every time.

def information_transfer()
  file_contents = CSV.read("test.csv", col_sep: ",", encoding: "ISO8859-1")
  file_contents2 = CSV.read("applicantinfo.csv", col_sep: ",", encoding: "ISO8859-1")

  h = Hash[file_contents.collect { |row| [row[0], row] }]

  CSV.open("language_output.csv", "wb") do |csv|
    for b in file_contents2
      a = h[b[0]]
      csv << a[0..18] + b[24..33]
    end
  end
end

Answer 3

Seems like one of file_contents or file_contents2 is empty.

You can skip the loop if you don't want to raise the error on that specific line.

next if file_contents[i].blank? || file_contents2[i].blank?
if file_contents[i][0] == file_contents2[x][0]