Delete an entire array in Ruby

Question

I'm trying to find out if I can delete an array with a method called on itself. array.clear removes all elements, but not the array itself.

Context

Here is the context. I have a CSV file with no headers. I want to be able to delete a row given one value in the row. So, the user can pass me "Chocolate", I seach the CSV and delete the row with Chocolate as the first value.

CSV file

Chocolate, some description blah
Cheese, some description about this one

Ruby file

require 'csv'

def remove_recipe(recipe_name)
  CSV.foreach(csv_file_path, w+) do |row|
    row.clear??? if row[0] == recipe_name
  end
end

I could add a header but I'd like to know if it's possible without.

Ok, to describe the input and output as Sawa has asked: A user will input string "Chocolate". I will search the CSV file for that string. If present, I want to update the CSV file to remove the row containing that string.

My edit undone. Do people not see that "post have been updated while you were editing" notification? :( — Sergio Tulentsev
– Sergio Tulentsev, Commented Oct 13, 2017 at 16:31
By the way my edit got stuck, wrapping around Sergio's edit, with edit #4 being empty. It looks like a bug on StackOverflow. — sawa
– sawa, Commented Oct 13, 2017 at 16:34

hoffm · Accepted Answer · 2017-10-13 16:36:53Z

3

Parse the CSV as an array of arrays and remove the elements you want to remove:

require "csv"

def remove_recipe(recipe_name)
  csv_ary = CSV.read("path/to/file.csv")
  cleaned_csv_ary = csv_ary.reject { |row| row[0] == recipe_name }
  # etc
end

Where I wrote "etc" you can use the cleaned array as you like, including converting it into a CSV string via #to_csv and writing it to a file.

answered Oct 13, 2017 at 16:36

hoffm

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8 Comments

tadman Over a year ago

Another option is to use reject! to remove them from the original array.

hoffm Over a year ago

Absolutely, @tadman. I just figured it'd be more readable to rename the var anyway.

tadman Over a year ago

I think the in-place modification steers closer to the intent in the original question: Deleting rows.

tadman Over a year ago

You can't avoid "parsing the file into an array", that's just how the CSV library works, and how Ruby works in general. You'll need to reject! and then re-write the file. Altering the array doesn't alter the source of that array, you need to explicitly write it out again.

Steve Midgley Over a year ago

As @tadman says, you can't just delete a row in the file and have all the following rows just "move one up" - that's not physically possible. You have to read the data into memory and flow them back down onto disk without the row in question. You could truncate the existing file to the row before the deleted row and stream the rest of the rows back out.

|

Derek Wright · Accepted Answer · 2017-10-13 17:53:29Z

2

If you are looking to update the CSV file, then this is the cleanest solution I could come up with:

require "csv"

def remove_recipe(name)
  rows = CSV.read('test.csv')
  rows.reject! { |r| r[0] == name }
  out = rows.inject([]) { |csv, row| csv << CSV.generate_line(row) }.join("")
  File.open('test.csv', 'w+') { |file| file.write(out) }
end

remove_recipe('Chocolate')

edited Oct 13, 2017 at 17:53

answered Oct 13, 2017 at 17:15

Derek Wright

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