Ruby CSV - get current line/row number
Because of changes in CSV in current Rubies, we need to make some changes. See farther down in the answer for the original solution with Ruby prior to 2.6. and the use of with_index
which continues to work regardless of the version.
For 2.6+ this'll work:
require 'csv'puts RUBY_VERSIONcsv_file = CSV.open('test.csv')csv_file.each do |csv_row| puts '%i %s' % [csv_file.lineno, csv_row]endcsv_file.close
If I read:
Year,Make,Model,Description,Price1997,Ford,E350,"ac, abs, moon",3000.001999,Chevy,"Venture ""Extended Edition""","",4900.001999,Chevy,"Venture ""Extended Edition, Very Large""","",5000.001996,Jeep,Grand Cherokee,"MUST SELL!\nair, moon roof, loaded",4799.00
The code results in this output:
2.6.31 ["Year", "Make", "Model", "Description", "Price"]2 ["1997", "Ford", "E350", "ac, abs, moon", "3000.00"]3 ["1999", "Chevy", "Venture \"Extended Edition\"", "", "4900.00"]4 ["1999", "Chevy", "Venture \"Extended Edition, Very Large\"", "", "5000.00"]5 ["1996", "Jeep", "Grand Cherokee", "MUST SELL!\\nair, moon roof, loaded", "4799.00"]
The change is because we have to get access to the current file handle. Previously we could use the global $.
, which always had a possibility of failure because globals can get stomped on by other sections of called code. If we have the handle of the file being opened, then we can use lineno
without that concern.
$.
Ruby prior to 2.6 would let us do this:
Ruby has a magic variable $.
which is the line number of the current file being read:
require 'csv'CSV.foreach('test.csv') do |csv| puts $.end
with the code above, I get:
12345
$INPUT_LINE_NUMBER
$.
is used all the time in Perl. In Ruby, it's recommended we use it the following way to avoid the "magical" side of it:
require 'english'puts $INPUT_LINE_NUMBER
If it's necessary to deal with embedded line-ends in fields, it's easily handled by a minor modification. Assuming a CSV file "test.csv" which contains a line with an embedded new-line:
Year,Make,Model,Description,Price1997,Ford,E350,"ac, abs, moon",3000.001999,Chevy,"Venture ""Extended Edition""","",4900.001996,Jeep,Grand Cherokee,"MUST SELL!air, moon roof, loaded",4799.001999,Chevy,"Venture ""Extended Edition, Very Large""","",5000.00
with_index
Using Enumerator's with_index(1)
makes it easy to keep track of the number of times CSV yields to the block, effectively simulating using $.
but honoring CSV's work when reading the extra lines necessary to deal with the line-ends:
require 'csv'CSV.foreach('test.csv', headers: true).with_index(1) do |row, ln| puts '%-3d %-5s %-26s %s' % [ln, *row.values_at('Make', 'Model', 'Description')]end
Which, when run, outputs:
$ ruby test.rb1 Ford E350 ac, abs, moon2 Chevy Venture "Extended Edition"3 Jeep Grand Cherokee MUST SELL!air, moon roof, loaded4 Chevy Venture "Extended Edition, Very Large"