Write an array to multi column CSV format using Ruby

Question

I have an array of arrays in Ruby that i'm trying to output to a CSV file (or text). That I can then easily transfer over to another XML file for graphing.

I can't seem to get the output (in text format) like so. Instead I get one line of data which is just a large array.

0,2
0,3
0,4
0,5

I originally tried something along the lines of this

File.open('02.3.gyro_trends.text' , 'w') { |file| trend_array.each { |x,y| file.puts(x,y)}}

And it outputs

0.2
46558
0
46560
0
....etc etc.

Can anyone point me in the "write" direction for getting either:

(i) .text file that can put my data like so.

trend_array[0][0], trend_array[0][1] 
trend_array[1][0], trend_array[1][1] 
trend_array[2][0], trend_array[2][1] 
trend_array[3][0], trend_array[3][1]

(ii) .csv file that would put this data in separate columns.
edit I recently added more than two values into my array, check out my answer combining Cameck's solution.

This is currently what I have at the moment.

trend_array=[]
j=1

# cycle through array and find change in gyro data.

while j < gyro_array.length-2

  if gyro_array[j+1][1] < 0.025 && gyro_array[j+1][1] > -0.025
    trend_array << [0, gyro_array[j][0]]
    j+=1
  elsif gyro_array[j+1][1] > -0.025  # if the next value is      increasing by x1.2 the value of the previous amount. Log it as +1
    trend_array << [0.2, gyro_array[j][0]]
    j+=1
  elsif gyro_array[j+1][1] <  0.025 # if the next value is   decreasing by x1.2 the value of the previous amount. Log it as -1
    trend_array << [-0.2, gyro_array[j][0]]
    j+=1
  end
end

#for graphing and analysis purposes (wanted to print it all as a csv  in two columns)

File.open('02.3test.gyro_trends.text' , 'w') { |file| trend_array.each { |x,y| file.puts(x,y)}}

File.open('02.3test.gyro_trends_count.text' , 'w') { |file| trend_array.each {|x,y| file.puts(y)}}

I know it's something really easy, but for some reason I'm missing it. Something with concatenation, but I found that if I try and concatenate a \\n in my last line of code, it doesn't output it to the file. It outputs it in my console the way I want it, but not when I write it to a file.

Thanks for taking the time to read this all.

tkupari · Accepted Answer · 2017-06-18 17:15:16Z

3

File.open('02.3test.gyro_trends.text' , 'w') { |file| trend_array.each { |a| file.puts(a.join(","))}}

answered Jun 18, 2017 at 17:15

tkupari

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3 Comments

Ryan Anderson Over a year ago

Wicked, I knew I was missing something so simple.

engineersmnky Over a year ago

@RyanAnderson as a note there is a CSV library in ruby's Standard Libraries that will facilitate this functionality for you. See CSV#add_row for more details. Writing Header will give you hints on how to implement this

Ryan Anderson Over a year ago

Thanks engineersmnky, everyone has been really helpful. Love the stack!

cameck · Accepted Answer · 2017-06-19 14:28:10Z

1

Alternately using the CSV Class:

  def write_to_csv(row)
    if csv_exists?
      CSV.open(@csv_name, 'a+') { |csv| csv << row }
    else
      # create and add headers if doesn't exist already
      CSV.open(@csv_name, 'wb') do |csv|
        csv << CSV_HEADER
        csv << row
      end
    end
  end

  def csv_exists?
    @exists ||= File.file?(@csv_name)
  end

Call write_to_csv with an array [col_1, col_2, col_3]

answered Jun 19, 2017 at 14:28

cameck

2,09822 silver badges34 bronze badges

2 Comments

Ryan Anderson Over a year ago

Cameck, you're the man! Thanks a lot. Exactly what I was looking for!

cameck Over a year ago

Awesome! Happy to help :)

Ryan Anderson · Accepted Answer · 2017-06-20 02:21:28Z

Thank you both @cameck & @tkupari, both answers were what I was looking for. Went with Cameck's answer in the end, because it "cut out" cutting and pasting text => xml. Here's what I did to get an array of arrays into their proper places.

require 'csv'

CSV_HEADER = [
                "Apples",
                "Oranges",
                "Pears"
                        ]

@csv_name = "Test_file.csv"

def write_to_csv(row)
  if csv_exists?
    CSV.open(@csv_name, 'a+') { |csv| csv << row }
  else
    # create and add headers if doesn't exist already
    CSV.open(@csv_name, 'wb') do |csv|
      csv << CSV_HEADER
      csv << row
    end
  end
end

def csv_exists?
  @exists ||= File.file?(@csv_name)
end

array = [ [1,2,3] , ['a','b','c'] , ['dog', 'cat' , 'poop'] ]
array.each { |row| write_to_csv(row) }

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