Given a string representing a matrix of numbers, return the rows and columns of that matrix.
So given a string with embedded newlines like:
9 8 7
5 3 2
6 6 7
representing this matrix:
0 1 2
|---------
0 | 9 8 7
1 | 5 3 2
2 | 6 6 7
your code should be able to spit out:
The rows for our example matrix:
And its columns:
For installation and learning resources, refer to the Ruby resources page.
For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:
gem install minitest
If you would like color output, you can require 'minitest/pride'
in
the test file, or note the alternative instruction, below, for running
the test file.
Run the tests from the exercise directory using the following command:
ruby matrix_test.rb
To include color from the command line:
ruby -r minitest/pride matrix_test.rb
Warmup to the saddle-points
warmup. http://jumpstartlab.com
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
require 'minitest/autorun'
require_relative 'matrix'
class MatrixTest < Minitest::Test
def test_extract_a_row
matrix = Matrix.new("1 2\n10 20")
assert_equal [1, 2], matrix.rows[0]
end
def test_extract_same_row_again
skip
matrix = Matrix.new("9 7\n8 6")
assert_equal [9, 7], matrix.rows[0]
end
def test_extract_other_row
skip
matrix = Matrix.new("9 8 7\n19 18 17")
assert_equal [19, 18, 17], matrix.rows[1]
end
def test_extract_other_row_again
skip
matrix = Matrix.new("1 4 9\n16 25 36")
assert_equal [16, 25, 36], matrix.rows[1]
end
def test_extract_a_column
skip
matrix = Matrix.new("1 2 3\n4 5 6\n7 8 9\n 8 7 6")
assert_equal [1, 4, 7, 8], matrix.columns[0]
end
def test_extract_another_column
skip
matrix = Matrix.new("89 1903 3\n18 3 1\n9 4 800")
assert_equal [1903, 3, 4], matrix.columns[1]
end
end
class Matrix
def initialize(matrix)
@matrix = matrix
end
def rows
@rows ||= @matrix.each_line.map { |item| item.split.map(&:to_i) }
end
def columns
rows.transpose
end
end
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Community comments
Thanks to this solution I realised I've missed doing better, namely - to calculate @rows lazily, on first invocation (@rows ||= ...) Just one note -- you can optimise columns method the same way: @colums ||= row.transpose
Thanks for your comment.
I didn't memoize
#columns
thinking that it's not called a second time in this class. But actually, being a public method, it may make sense to also do it.