How to sequentially create multiple CSV files in Ruby?

Question

Silly question, but I want to do some processing on a dataset and put them into different CSVs, like UDID1.csv, UDID2.csv, ..., UDID1000.csv. So this is my code:

for i in 1..1000
    logfile = File.new('C:\Users\hp1\Desktop\Datasets\New File\UDID#{i}\.csv',"a")
    #I'll do some processing here
end

But the program throws an error when running because of the UDID#{i} part. So, how to overcome this issue? Thanks.

Edit: This is the error:

in `initialize': No such file or directory @ rb_sysopen - C:\Users\hp1\Desktop\Datasets\New File\udid#{1}\.csv (Errno::ENOENT)from C:/Ruby21/bin/hashedUDID.rb:38:in `new' from C:/Ruby21/bin/hashedUDID.rb:38:in '<main>'

knut · Accepted Answer · 2015-09-30 11:40:47Z

2

The ' is one problem, another problem is the path.

In your posting the New File must exist as a directory. Inside this directory must exist another directories like UDID0001. This gets a .csv file.

Correct is (I don't use the non-rubyesk for-loop):

1.upto(1000) do |i|
    logfile = File.new("C:\\Users\\hp1\\Desktop\\Datasets\\UDID#{i}.csv", "a")
    #I'll do some processing here
    logfile.close #Don't forget to close the file
end

Inside " the backslash must be masked (\\). Instead you may use /:

logfile = File.new("C:/Users/hp1/Desktop/Datasets/New File/UDID#{i}/.csv", "a")

Another possibility is the usage of %i to insert the number:

    logfile = File.new("C:/Users/hp1/Desktop/Datasets/New File/UDID%02i/.csv" % i, "a")

I prefer to use open, then the file is closed with the end of the block:

    File.open("C:/Users/hp1/Desktop/Datasets/New File/UDID%04i/.csv" % i, "a") do |logfile|
      #I'll do some processing here
    end #closes the file

Warning:

I'm not sure, if you really want to create 1000 log files (The File is opened inside the loop. so each step creates a file.). If yes, then the %04i-version has the advantage, that the files get all the same number of digits (starting with 0001 and ending with 1000).

edited Sep 30, 2015 at 11:40

answered Sep 30, 2015 at 11:35

knut

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3 Comments

Kristada673 Over a year ago

Ok, that worked! Thanks! As for why I need this, actually my original problem can be found here: stackoverflow.com/questions/32797346/… So, because the hashed array can't store so many values, I thought of partitioning my dataset into smaller manageable chunks, hashing them, storing them in separate CSV files (which is this question), & then compare them with subsequent hashings.

knut Over a year ago

If this answer solves the problem of your question you should accept the answer.

davegson Over a year ago

for a thorough solution +1

Sergio Tulentsev · Accepted Answer · 2015-09-30 11:43:56Z

0

(1..10).each { |i| logfile = File.new("/base/path/UDID#{i}.csv") }

You must use double quote (") when you need string interpolation.

edited Sep 30, 2015 at 11:43

Sergio Tulentsev

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answered Sep 30, 2015 at 11:23

Sayuj

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1 Comment

davegson Over a year ago

how does this add to my existing answer?

davegson · Accepted Answer · 2015-09-30 12:23:24Z

0

#{} can only be used in strings with double quotes ". So change your code to:

for i in 1..1000
  logfile = File.new("C:\Users\hp1\Desktop\Datasets\New File\UDID#{i}\.csv","a")
  # other stuff
end

edited Sep 30, 2015 at 12:23

answered Sep 30, 2015 at 11:20

davegson

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1 Comment

Sergio Tulentsev Over a year ago

Except that #{} is not a constructor :)

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