Ruby - comparing adjacent entries in one column of a csv file - ruby

Question

I'm new to Ruby, so apologies if this is dead easy :-)
I have a .csv file with 5 columns. The first column has a record identifier (in this case a driver number) and the other 4 columns in each row have data relating to that record. For each record there are around 50 rows of data (just under 2,000 rows in total). The .csv file has a header row.
I need to read the .csv file and identify the last entry for each user, so I can move on to the next user. I've tried to get it to compare the first column and the entry in the next row.
I have this so far, it returns incorrect row numbers and they're anywhere between 1 and 5 rows out...?!?!
require 'csv-mapper'
Given(/^I compare the driver numbers from rows "(.*?)" to "(.*?)"$/) do |firstrow, lastrow|
data = CsvMapper.import('C:/auto_test_data/Courts code example csv.csv', headers: true) do
[dln]
end
row = firstrow.to_i
while row <= lastrow.to_i
#licnum1 = data.at(row).dln
#licnum2 = data.at(row+1).dln
if
#licnum2 == #licnum1
$newrecord = "same"
else
$newrecord = #licnum2
end
if
$newrecord != "same"
puts "Last row for #{#licnum1} is #{row}\n"
end
row = row + 1
end
end
This is the layout for the .csv file:
recordidentifier1 dataitem1 dataitem2 code descriptionforcomparison
recordidentifier1 dataitem1 dataitem2 code descriptionforcomparison
recordidentifier2 dataitem1 dataitem2 code descriptionforcomparison
recordidentifier2 dataitem1 dataitem2 code descriptionforcomparison
All help will be greatly appreciated.
Thanks,
Peter

Answer 1

Here's one way to do it
current_identifier = nil
(firstrow.to_i..lastrow.to_i).each do |row|
if current_identifer != data.at(row).dln # current row is new identifier
if current_identifier # this is not the first row
puts "Last row for #{current_identifier} is #{row-1}\n"
end
current_identifier = data.at(row).dln # remember current row
end
# we need to track the last row as the last for the current identifier
puts "Last row for #{current_identifier} is #{lastrow.to_i}\n"