How can I skip the header row when reading a CSV in Ruby?

Question

Ruby's CSV class makes it pretty easy to iterate over each row:

CSV.foreach(file) { |row| puts row }

However, this always includes the header row, so I'll get as output:

header1, header2
foo, bar
baz, yak

I don't want the headers though. Now, when I call …

CSV.foreach(file, :headers => true)

I get this result:

#<CSV::Row:0x10112e510
    @header_row = false,
    attr_reader :row = [
        [0] [
            [0] "header1",
            [1] "foo"
        ],
        [1] [
            [0] "header2",
            [1] "bar"
        ]
    ]
>

Of course, because the documentation says:

This setting causes #shift to return rows as CSV::Row objects instead of Arrays

But, how can I skip the header row, returning the row as a simple array? I don't want the complicated CSV::Row object to be returned.

I definitely don't want to do this:

first = true
CSV.foreach(file) do |row|
  if first
    puts row
    first = false
  else
    # code for other rows
  end
end

check http://stackoverflow.com/a/37856698/473040 – equivalent8 Jun 16 '16 at 10:35 — equivalent8, Jun 16 '16 at 10:35

score 16 · Answer 1 · answered Jul 31 '12 at 12:57

16

Look at #shift from CSV Class:

The primary read method for wrapped Strings and IOs, a single row is pulled from the data source, parsed and returned as an Array of fields (if header rows are not used)

An Example:

require 'csv'

# CSV FILE
# name, surname, location
# Mark, Needham, Sydney
# David, Smith, London

def parse_csv_file_for_names(path_to_csv)
  names = []  
  csv_contents = CSV.read(path_to_csv)
  csv_contents.shift
  csv_contents.each do |row|
    names << row[0]
  end
  return names
end

answered Jul 31 '12 at 12:57

waldyr.ar

14,424
6
33
64

CSV.read returns ans Array and #shift is default methods for array. and correctfully very usefull here. – Pritesh Jain Jul 31 '12 at 13:53
You can also iterate using `each_with_index` and check which line index you're on. A `next if (i == 0)` would skip the first line for index `i`. – tadman Jul 31 '12 at 15:59
@tadman Feel free to post that as a separate answer – looks viable. – slhck Aug 01 '12 at 11:31
Is this more memory intensive because you're saving the entire file contents into a variable, as opposed to reading line by line when doing foreach? – ahnbizcad Aug 30 '16 at 18:42

score 16 · Answer 2 · edited May 23 '17 at 12:02

16

You might want to consider CSV.parse(csv_file, { :headers => false }) and passing a block, as mentioned here

edited May 23 '17 at 12:02

Community

1
1

answered Jul 31 '12 at 21:08

jodell

1,057
9
20

1

note: this only works since Ruby 1.9 – inger May 15 '13 at 16:42
19

additional note: if you're using < Ruby 1.9 then you really should update. – ocodo Dec 16 '13 at 23:33
2

This didn't seem to work for me. I had to do `CSV.parse(csv_file, headers: :first_row, return_headers: false)` to get it working. – aardvarkk May 22 '19 at 22:59
@ocodo Based and Redpilled. – Patricio Sard Nov 04 '20 at 20:05

score 9 · Answer 3 · answered Dec 16 '13 at 23:30

9

A cool way to ignore the headers is to read it as an array and ignore the first row:

data = CSV.read("dataset.csv")[1 .. -1]
# => [["first_row", "with data"],
      ["second_row", "and more data"],
      ...
      ["last_row", "finally"]]

The problem with the :headers => false approach is that CSV won't try to read the first row as a header, but will consider it part of the data. So, basically, you have a useless first row.

answered Dec 16 '13 at 23:30

Carlos Agarie

3,952
1
26
38

Nice to see a few options, but keep in mind if your CSV file is large, this isn't very memory-friendly relative to the other answers. Also, it's exactly the same answer as [this](https://stackoverflow.com/a/20623072/6243352) -- best to post once. – ggorlen Oct 05 '21 at 23:51

How can I skip the header row when reading a CSV in Ruby?

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