How do I read a text file into an array of array (each sub-array being a row in the text file?)

Question

so I'm pretty much a n00b at Ruby, and I've put together a code to solve a MinCut problem (for an assignment, yes - that part of the code I've put together and tested), and I can't figure out how to read a file and put it into an array of arrays. I have a text file to read, with columns of varying length as below

1 37 79 164

2 123 134

3 48 123 134 109

and I'd like to read it into a 2D array, where each line and columnn is split, with each line going into one array. So the resulting array for the above example would be :

[[1, 37, 79, 164], [2, 123, 134], [3, 48, 123, 134, 109]]

My code to read the text file is below:

def read_array(file, count)
  int_array = []
  File.foreach(file) do |f|
    counter = 0
    while (l = f.gets and counter < count ) do
      temp_array = []
      temp_array << l.to_i.split(" ")
      int_array << temp_array
      counter = counter + 1
    end

  end
  return int_array
end

Any help is greatly appreciated!

Also, if it helps, the error I'm currently getting is "block in read_array': private method 'gets' called for # "

I've tried a few things, and have gotten different error messages though...

tessi · Accepted Answer · 2014-03-04 15:46:22Z

24

File.readlines('test.txt').map do |line|
  line.split.map(&:to_i)
end

Explanation

readlines reads the whole file and splits it by newlines. It looks like this:

["1 37 79 164\n", "2 123 134\n", "3 48 123 134 109"]

Now we iterate over the lines (using map) and split each line into its number parts (split)

[["1", "37", "79", "164"], ["2", "123", "134"], ["3", "48", "123", "134", "109"]]

The items are still strings, so the inner map converts them to integers (to_i).

[[1, 37, 79, 164], [2, 123, 134], [3, 48, 123, 134, 109]]

edited Mar 4, 2014 at 15:46

answered Jul 26, 2013 at 14:31

tessi

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2 Comments

winklerrr Over a year ago

What is the &: for?

tessi Over a year ago

.map(&:to_i) is equivalent to .map { |s| s.to_i }. More specifically, the & calls to_proc on the symbol. See: ruby-doc.org/core-2.3.1/Symbol.html#method-i-to_proc

Chowlett · Accepted Answer · 2013-07-26 14:27:20Z

11

Ruby's got you covered with just a few lines:

tmp.txt

1 2 3
10 20 30 45
4 2

Ruby code

a = []
File.open('tmp.txt') do |f|
  f.lines.each do |line|
    a << line.split.map(&:to_i)
  end
end

puts a.inspect
# => [[1, 2, 3], [10, 20, 30, 45], [4, 2]]

answered Jul 26, 2013 at 14:27

Chowlett

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1 Comment

Howzlife17 Over a year ago

Thank you so much! That's why I'm loving ruby, every time I'm having trouble with something the answer turns out to be much easier than previously thought

toro2k · Accepted Answer · 2013-07-26 14:40:22Z

2

The error in your code occurs because you are calling the method gets on the object f, which is a String, not a File as you would expected (check the documentation for IO#foreach for more informations).

Instead of fixing your code I suggest you to rewrite it in a simpler and more Rubyish style, I'd write it like this:

def read_array(file_path)
  File.foreach(file_path).with_object([]) do |line, result|
    result << line.split.map(&:to_i)
  end
end

Given this file.txt:

1 37 79 164
2 123 134
3 48 123 134 109

It produce this output:

read_array('file.txt')
# => [[1, 37, 79, 164], [2, 123, 134], [3, 48, 123, 134, 109]]

edited Jul 26, 2013 at 14:40

answered Jul 26, 2013 at 14:32

toro2k

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1 Comment

tessi Over a year ago

+1 for explaining the error he got. The rest of us forgot that :)

Reza · Accepted Answer · 2016-03-26 07:05:14Z

1

array_line = []  

if File.exist? 'test.txt'
  File.foreach( 'test.txt' ) do |line|
      array_line.push line
  end
end

answered Mar 26, 2016 at 7:05

Reza

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1 Comment

Benjamin W. Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.

lurker · Accepted Answer · 2013-07-26 14:33:56Z

0

def read_array(file)
  int_array = []

  File.open(file, "r").each_line { |line| int_array << line.split(' ').map {|c| c.to_i} }

  int_array
end

edited Jul 26, 2013 at 14:33

answered Jul 26, 2013 at 14:27

lurker

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