Ruby csv - delete row if column is empty

Trying to delete rows from the csv file here with Ruby without success.

How can I tell that all rows, where column "newprice" is empty, should be deleted?

require 'csv' 
guests = CSV.table('new.csv', headers:true)

guests.each do |guest_row|
  p guests.to_s 
end

price = CSV.foreach('new.csv', headers:true) do |row|
  puts row['newprice'] 
end 

guests.delete_if('newprice' = '')

File.open('new_output.csv', 'w') do |f|
  f.write(guests.to_csv)
end

Thanks!