In Ruby, how to read data column wise from a CSV file?

Question

I know how it is done row-wise

CSV.foreach(filename.csv) do |row|
  puts \"#{row}\"
end

But I am completely lost column wise?

Answer 1

test.csv:

name,surname,no1,no2,no3,date
Raja,Palit,77489,24,84,12/12/2011
Mathew,bargur,77559,25,88,01/12/2011
harin,Roy,77787,24,80,12/12/2012
Soumi,paul,77251,24,88,11/11/2012

Acces by cols:

require 'csv'
csv = CSV.read('test.csv', :headers=>true)
p csv['name'] #=>["Raja", "Mathew", "harin", "Soumi"]

#or even:
t = CSV.table('test.csv')
p t[:no1] #=> [77489, 77559, 77787, 77251]

Note that in the last case the cols are accessed by their symbolized name and that strings are converted to numbers when possible.

Answer 2

This is the solution guys:

CSV.foreach(filename).map { |row| row[0] }

Sorry for posting it in the correct format so late.

Answer 3

Bored so decided to cook up an alternate solution here. Only works (here) if the first row has the max number of columns

columns = {}
rows.first.each_with_index do |col, i|
  columns[i] = []
end
rows.each do |row|
  row.each_with_index do |cell, i|
    columns[i] = columns[i] + [cell]
  end
end

Now you should be able to access each column by its index

Answer 4

The method 'by_col' provides you output based on your column selection.

test_csv:

name,surname,no1,no2,no3,date
Raja,Palit,77489,24,84,12/12/2011
Mathew,bargur,77559,25,88,01/12/2011
harin,Roy,77787,24,80,12/12/2012
Soumi,paul,77251,24,88,11/11/2012

Code:

CSV.parse(File.open('test_csv'), headers: true).by_col['surname']

Output:

['Palit','bargur','Roy','paul']

Answer 5

Transpose your CSV file. By doing this your rows covert to column and viceversa. Below a simple example of transpose.

   irb(main):001:0> [["1", "2", "3"], ["4", "5", "6"], ["7", "8", "9"]].transpose
    => [["1", "4", "7"], ["2", "5", "8"], ["3", "6", "9"]]