Ruby undefined method `[]' for nil:NilClass (NoMethodError) error - ruby-on-rails

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

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]

Answer 2

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 3

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