How to print a 2D array with fixed column width - arrays

Question

I have an array:
animals = [
["cats", "dogs"],
["verrylongcat", "dog"],
["shortcat", "verrylongdog"],
["cat", "dog"]
]
And I would like to display it nicely. Is there an easy way to make the colums a fixed width so I get something like this:
cats dogs
verrylongcat dog
shortcat verrylongdog
cat dog
animals is just an example, my array could also have 3, or 4 columns or even more.

Answer 1

You are looking for String#ljust:
max_cat_size = animals.map(&:first).max_by(&:size).size
animals.each do |cat, dog|
puts "#{cat.ljust(max_cat_size)} #{dog}"
end
If you want more than one space just add the corresponding amount in the interpolation.
Assuming your array is n × m and not 2 × m:
animal_max_sizes = animals.first.size.times.map do |index|
animals.transpose[index].map(&:to_s).max_by(&:size).size
end
animals.map do |animal_line|
animal_line.each.with_index.reduce('') do |animal_line, (animal, index)|
animal_line + animal.to_s.ljust(animal_max_sizes[index].next)
end
end.each { |animal_line_stringified| puts animal_line_stringified }
Note: The to_ses are used in case your arrays contain nils, numbers, etc.

Answer 2

Another way to do this is with printf-style formatting. If you know you will always have exactly 2 words in each line then you can do this:
#!/usr/bin/env ruby
lines = [
' cats dogs',
' verrylongcat dog',
'shortcat verrylongdog ',
' cat dog ',
]
lines.map(&:strip).each do |line|
puts "%-14s%s" % line.split
end
Outputs:
cats dogs
verrylongcat dog
shortcat verrylongdog
cat dog
If you need to calculate the column width based on the data, then you'd have to do a little more work:
# as #ndn showed:
first_col_width = lines.map(&:split).map(&:first).max_by(&:size).size + 2
lines.map(&:strip).each do |line|
puts "%-#{first_col_width}s%s" % line.split
end

Answer 3

Here's another attempt for a variable numbers of columns. Given this array:
animals = [
['Cats', 'Dogs', 'Fish'],
['Mr. Tinkles', 'Buddy', 'Nemo'],
['Calico', 'Butch', 'Marlin'],
['Ginger', 'Ivy', 'Dory']
]
We can calculate the width of each column via transpose, map, length and max:
widths = animals.transpose.map { |x| x.map(&:length).max }
#=> [11, 5, 6]
Based on this, we can generate a format string that can be passed to sprintf (or its shortcut %):
row_format = widths.map { |w| "%-#{w}s" }.join(' ')
#=> "%-11s %-5s %-6s"
%s denotes a string argument, 11, 5 and 6 are our widths and - left-justifies the result.
Let's try it:
row_format % animals[0] #=> "Cats Dogs Fish "
row_format % animals[1] #=> "Mr. Tinkles Buddy Nemo "
row_format % animals[2] #=> "Calico Butch Marlin"
That looks good, we should use a loop and wrap everything it in a method:
def print_table(array)
widths = array.transpose.map { |x| x.map(&:length).max }
row_format = widths.map { |w| "%-#{w}s" }.join(' ')
array.each do |row_values|
puts row_format % row_values
end
end
print_table(animals)
Output:
Cats Dogs Fish
Mr. Tinkles Buddy Nemo
Calico Butch Marlin
Ginger Ivy Dory
More complex formatting
With a little tweaking, you can also output a MySQL style table:
def print_mysql_table(array)
widths = array.transpose.map { |x| x.map(&:length).max }
row_format = '|%s|' % widths.map { |w| " %-#{w}s " }.join('|')
separator = '+%s+' % widths.map { |w| '-' * (w+2) }.join('+')
header, *rows = array
puts separator
puts row_format % header
puts separator
rows.each do |row_values|
puts row_format % row_values
end
puts separator
end
print_mysql_table(animals)
Output:
+-------------+-------+--------+
| Cats | Dogs | Fish |
+-------------+-------+--------+
| Mr. Tinkles | Buddy | Nemo |
| Calico | Butch | Marlin |
| Ginger | Ivy | Dory |
+-------------+-------+--------+