c# barcode reader reading and Searching CSV Data in C#

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The CSV class provided by the csv standard library will manage the manipulation of CSV data for you: require 'csv' CSV.open('text.txt', 'r').each do |person| puts person.inspect end
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["Fred Bloggs", "Manager", "Male", "45"] ["Laura Smith", "Cook", "Female", "23"] ["Debbie Watts", "Professor", "Female", "38"] You open the text.txt file by using CSV.open, and each line (that is, each individual person in the file) is passed into the block one by one using each. The inspect method demonstrates that each entry is now represented in array form. This makes it easier to read the data than when it was in its plain text form. You can also use CSV alongside the File class: require 'csv' people = CSV.parse(File.read('text.txt')) puts people[0][0] puts people[1][0] puts people[2][0]
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Fred Bloggs Laura Smith Debbie Watts
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C h a p t e r 9 F I Le S a N D D a t a B a S e S
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This example uses the File class to open and read in the contents of a file, and CSV.parse immediately uses these to convert the data into an array of arrays. The elements in the main array represent each line in the file, and each element in those elements represents a different attribute (or field) of that line. Therefore, by printing out the first element of each entry, you get the people s names only. An even more succinct way of loading the data from a CSV-formatted file into an array is with CSV.read: puts CSV.read('text.txt').inspect
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[["Fred Bloggs", "Manager", "Male", "45"], ["Laura Smith", "Cook", "Female", "23"], ["Debbie Watts", "Professor", "Female", "38"]] The find and find_all methods (also known as detect and select, respectively) provided by the Enumerable module to Array make it easy for you to perform searches upon the data available in the array. For example, you d use this code if you wanted to pick out the first person in the data called Laura: require 'csv' people = CSV.read('text.txt') laura = people.find { |person| person[0] =~ /Laura/ } puts laura.inspect
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["Laura Smith", "Cook", "Female", "23"] Using the find (or detect) method with a code block that looks for the first matching line where the name contains Laura gives you back the data you were looking for. Where find returns the first matching element of an array or hash, find_all (or select) returns all valid matches. Let s say you want to find the people in your database whose ages are between 20 and 40: young_people = people.find_all do |p| p[3].to_i.between (20, 40) end puts young_people.inspect
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[["Laura Smith", "Cook", "Female", "23"], ["Debbie Watts", "Professor", "Female", "38"]] This operation provides you with the two matching people contained within an array that you can iterate through.
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Saving Data Back to the CSV File
Once you can read and query data, the next step is being able to change it, delete it, and rewrite your CSV file with a new version of the data for future use. Luckily, this is as simple
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as reopening the file with write access and pushing the data back to the file. The CSV module handles all of the conversion. require 'csv' people = CSV.read('text.txt') laura = people.find { |person| person[0] =~ /Laura/ } laura[0] = "Lauren Smith" CSV.open('text.txt', 'w') do |csv| people.each do |person| csv << person end end You load in the data, find a person to change, change her name, and then open up the CSV file and rewrite the data back to it. Notice, however, that you have to write the data person by person. Once complete, text.txt is updated with the name change. This is how to write back CSV data to file. ( 17 provides more information about CSV, along with information about FasterCSV, a faster CSV implementation for Ruby 1.8 that s available as a library.)
note FasterCSV became the standard CSV library in Ruby 1.9 and is no longer referred to as FasterCSV
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