How to map and edit a CSV file with Ruby - ruby

Question

Is there a way to edit a CSV file using the map method in Ruby? I know I can open a file using:
CSV.open("file.csv", "a+")
and add content to it, but I have to edit some specific lines.
The foreach method is only useful to read a file (correct me if I'm wrong).
I checked the Ruby CSV documentation but I can't find any useful info.
My CSV file has less than 1500 lines so I don't mind reading all the lines.

Answer 1

Another answer using each.with_index():
rows_array = CSV.read('sample.csv')
desired_indices = [3, 4, 5].sort # these are rows you would like to modify
rows_array.each.with_index(desired_indices[0]) do |row, index|
if desired_indices.include?(index)
# modify over here
rows_array[index][target_column] = 'modification'
end
end
# now update the file
CSV.open('sample3.csv', 'wb') { |csv| rows_array.each{|row| csv << row}}
You can also use each_with_index {} insead of each.with_index {}

Answer 2

Is there a way to edit a CSV file using the map method in Ruby?
Yes:
rows = CSV.open('sample.csv')
rows_array = rows.to_a
or
rows_array = CSV.read('sample.csv')
desired_indices = [3, 4, 5] # these are rows you would like to modify
edited_rows = rows_array.each_with_index.map do |row, index|
if desired_indices.include?(index)
# simply return the row
# or modify over here
row[3] = 'shiva'
# store index in each edited rows to keep track of the rows
[index, row]
end
end.compact
# update the main row_array with updated data
edited_rows.each{|row| rows_array[row[0]] = row[1]}
# now update the file
CSV.open('sample2.csv', 'wb') { |csv| rows_array.each{|row| csv << row}}
This is little messier. Is not it? I suggest you to use each_with_index with out map to do this. See my another answer

Answer 3

Here is a little script I wrote as an example on how read CSV data, do something to data, and then write out the edited text to a new file:
read_write_csv.rb:
#!/usr/bin/env ruby
require 'csv'
src_dir = "/home/user/Desktop/csvfile/FL_insurance_sample.csv"
dst_dir = "/home/user/Desktop/csvfile/FL_insurance_sample_out.csv"
puts " Reading data from : #{src_dir}"
puts " Writing data to : #{dst_dir}"
#create a new file
csv_out = File.open(dst_dir, 'wb')
#read from existing file
CSV.foreach(src_dir , :headers => false) do |row|
#then you can do this
# newrow = row.each_with_index { |rowcontent , row_num| puts "# {rowcontent} #{row_num}" }
# OR array to hash .. just saying .. maybe hash of arrays..
#h = Hash[*row]
#csv_out << h
# OR use map
#newrow = row.map(&:capitalize)
#csv_out << h
#OR use each ... Add and end
#newrow.each do |k,v| puts "#{k} is #{v}"
#Lastly, write back the edited , regexed data ..etc to an out file.
#csv_out << newrow
end
# close the file
csv_out.close
The output file has the desired data:
USER#USER-SVE1411EGXB:~/Desktop/csvfile$ ls
FL_insurance_sample.csv FL_insurance_sample_out.csv read_write_csv.rb
The input file data looked like this:
policyID,statecode,county,eq_site_limit,hu_site_limit,fl_site_limit,fr_site_limit,tiv_2011,tiv_2012,eq_site_deductible,hu_site_deductible,fl_site_deductible,fr_site_deductible,point_latitude,point_longitude,line,construction,point_granularity
119736,FL,CLAY COUNTY,498960,498960,498960,498960,498960,792148.9,0,9979.2,0,0,30.102261,-81.711777,Residential,Masonry,1
448094,FL,CLAY COUNTY,1322376.3,1322376.3,1322376.3,1322376.3,1322376.3,1438163.57,0,0,0,0,30.063936,-81.707664,Residential,Masonry,3
206893,FL,CLAY COUNTY,190724.4,190724.4,190724.4,190724.4,190724.4,192476.78,0,0,0,0,30.089579,-81.700455,Residential,Wood,1
333743,FL,CLAY COUNTY,0,79520.76,0,0,79520.76,86854.48,0,0,0,0,30.063236,-81.707703,Residential,Wood,3
172534,FL,CLAY COUNTY,0,254281.5,0,254281.5,254281.5,246144.49,0,0,0,0,30.060614,-81.702675,Residential,Wood,1