Create array from csv using readlines ruby

Question

I can’t seem to get this to work

I know I can do this with csv gem but Im trying out new stuff and I want to do it this way. All Im trying to do is to read lines in from a csv and then create one array from each line. I then want to put the second element in each array.

So far I have

filed="/Users/me/Documents/Workbook3.csv"

if File.exists?(filed)
  File.readlines(filed).map {|d| puts d.split(",").to_a}
else puts "No file here”

The problem is that this creates one array which has all the lines in it whereas I want a separate array for each line (perhaps an array of arrays?) Test data

Trade date,Settle date,Reference,Description,Unit cost (p),Quantity,Value (pounds)
04/09/2014,09/09/2014,S5411,Plus500 Ltd ILS0.01 152 @  419,419,152,624.93
02/09/2014,05/09/2014,B5406,Biomarin Pharmaceutical Com Stk USD0.001 150 @  4284.75,4284.75,150,-6439.08
29/08/2014,03/09/2014,S5398,Hargreaves Lansdown plc Ordinary 0.4p 520 @  1116.84,1116.84,520,5795.62

What I would like

S5411
B5406
S5398

I still get the problem that its treated as one line so I just get one array. Perhaps readlines ignores newlines or something? — Sebastian Zeki
– Sebastian Zeki, Commented Sep 11, 2015 at 7:02
readlines is of course aware of newlines, that's the whole point ;-) Please show your output. — Stefan
– Stefan, Commented Sep 11, 2015 at 7:04

Cary Swoveland · Accepted Answer · 2015-09-11 07:12:24Z

2

Let write your data to a file:

s =<<THE_BITTER_END
Trade date,Settle date,Reference,Description,Unit cost (p),Quantity,Value (pounds)
04/09/2014,09/09/2014,S5411,Plus500 Ltd ILS0.01 152 @  419,419,152,624.93
02/09/2014,05/09/2014,B5406,Biomarin Pharmaceutical Com Stk USD0.001 150 @  4284.75,4284.75,150,-6439.08
29/08/2014,03/09/2014,S5398,Hargreaves Lansdown plc Ordinary 0.4p 520 @  1116.84,1116.84,520,5795.62
THE_BITTER_END

IO.write('temp',s)
  #=> 363

We can then do this:

arr = File.readlines('temp').map { |s| s.split(',') }
  #=> [["Trade date", "Settle date", "Reference", "Description", "Unit cost (p)",
        "Quantity", "Value (pounds)\n"],
       ["04/09/2014", "09/09/2014", "S5411",
        "Plus500 Ltd ILS0.01 152 @  419", "419", "152", "624.93\n"],
       ["02/09/2014", "05/09/2014", "B5406",
        "Biomarin Pharmaceutical Com Stk USD0.001 150 @  4284.75",
        "4284.75", "150", "-6439.08\n"],
       ["29/08/2014", "03/09/2014", "S5398",
        "Hargreaves Lansdown plc Ordinary 0.4p 520 @  1116.84", "1116.84",
        "520", "5795.62\n"]]

The values you want begin in the second element of arr and is the third element in each of those arrays. Therefore, you can pluck them out as follows:

arr[1..-1].map { |a| a[2] }
  #=> ["S5411", "B5406", "S5398"]

Adopting @Stefan's suggestion of putting [2] within the block containing split, we can write this more compactly as follows:

File.readlines('temp')[1..-1].map { |s| s.split(',')[2] }
  #=> ["S5411", "B5406", "S5398"]

edited Sep 11, 2015 at 7:12

answered Sep 11, 2015 at 7:06

Cary Swoveland

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4 Comments

Sebastian Zeki Over a year ago

I'm not sure that I understand why you have to write it to a temporary file before reading it in

Stefan Over a year ago

@SebastianZeki an example should be "self contained", i.e. it should include all the code and data that's needed to run it. See sscce.org

Sebastian Zeki Over a year ago

@Cary Why you have to write it to a temporary file before reading it in. Is it something to do with csv newlines?

Cary Swoveland Over a year ago

Sebastian, I didn't have to. I could have assumed you read the file containing the string I called s in the heredoc.I did it for the reason @Stefan gave. It was only one extra line. It had nothing to do with CSV.

Wand Maker · Accepted Answer · 2015-09-11 10:24:49Z

2

You can also use built-in class CSV to do this very easily.

require "csv"

s =<<THE_BITTER_END
Trade date,Settle date,Reference,Description,Unit cost (p),Quantity,Value (pounds)
04/09/2014,09/09/2014,S5411,Plus500 Ltd ILS0.01 152 @  419,419,152,624.93
02/09/2014,05/09/2014,B5406,Biomarin Pharmaceutical Com Stk USD0.001 150 @  4284.75,4284.75,150,-6439.08
29/08/2014,03/09/2014,S5398,Hargreaves Lansdown plc Ordinary 0.4p 520 @  1116.84,1116.84,520,5795.62
THE_BITTER_END

arr = CSV.parse(s, :headers=>true).collect { |row| row["Reference"] }
p arr
#=> ["S5411", "B5406", "S5398"]

PS: I have borrowed the string from @Cary's answer

answered Sep 11, 2015 at 10:24

Wand Maker

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1 Comment

engineersmnky Over a year ago

This is a much cleaner solution especially given the fact that the OP stated a CSV file. This is a great example of an XY Problem and answer

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