Question

I am new to ruby. I am trying to parse phone numbers from a CSV file and I did that using the following code. It is working properly.

require 'csv' 
csv_text = File.read('file.csv')
csv = CSV.parse(csv_text, :headers => true)
csv.each do |row|                                      
    puts "Home Phone: #{row['HomePhone']}"
end

What I want is to clean up HomePhone in the following ways.

1. If phone number has 10 digits, it is good, print it as such.
2. If phone number has less than 10 digits, print invalid number as “0000000000”
3. If phone number has 11 digits and first digit is 1, print last 10 digits (remove first 1), else “0000000000”

I don’t know how to do this.

Answer 1

You can get the length of a string with the aptly-named length method:

string = 'foobar'
string.length # => 6

You can check if a string starts with another string using start_with?:

string.start_with?('f') # => true

You can slice a string individual characters using array index notation (square brackets) and a range. A negative index counts from the end of the string. So to return all but the first character:

string[1..-1] # => 'oobar'

So to do what you are asking you can combine these

home_phone = row['HomePhone']
if home_phone.length == 10
  puts home_phone
elsif home_phone.length == 11 && home_phone.start_with?('1')
  puts home_phone[1..-1]
else
  puts '0000000000'
end

Note that this approach assumes that your phone numbers are already strings of digits and you just need to check their length. If you wanted to be more thorough and check for invalid phone numbers containing non-digits, like 123z567890, you might consider a regex approach:

if match = /^1?(?<number>\d{10})$/.match(row['HomePhone'])
  puts match[:number]
else
  puts '0000000000'
end

The components that this regex matches are:

• ^ – the start of the string
• 1? – an optional 1
• (?<number>\d{10}) – 10 digits (ie \d{10}) saved in a group called number
• $ – the end of the string

Ruby uses the forward slashes to delimit the regex, and the match method returns an object that we can use to extract the saved 10-digit number.