Truncate string when it is too long

Question

I have two strings:

short_string = "hello world"
long_string = "this is a very long long long .... string" # suppose more than 10000 chars

I want to change the default behavior of print to:

puts short_string
# => "hello world"
puts long_string
# => "this is a very long long....."

The long_string is only partially printed. I tried to change String#to_s, but it didn't work. Does anyone know how to do it like this?

updated

Actually i wanna it works smoothly, that means the following cases also work fine:

> puts very_long_str
> puts [very_long_str]
> puts {:a => very_long_str}

So i think the behavior belongs to String.

Thanks all anyway.

Doane

Answer 1

First of all, you need a method to truncate a string, either something like:

def truncate(string, max)
  string.length > max ? "#{string[0...max]}..." : string
end

Or by extending String: (it's not recommended to alter core classes, though)

class String
  def truncate(max)
    length > max ? "#{self[0...max]}..." : self
  end
end

Now you can call truncate when printing the string:

puts "short string".truncate
#=> short string

puts "a very, very, very, very long string".truncate
#=> a very, very, very, ...

Or you could just define your own puts:

def puts(string)
  super(string.truncate(20))
end

puts "short string"
#=> short string

puts "a very, very, very, very long string"
#=> a very, very, very, ...

Note that Kernel#puts takes a variable number of arguments, you might want to change your puts method accordingly.

Willy

If the string is nearly at max, then the ellipsis will put it over. You need something like: string.length > max ? "#{string[0...(max-3)]}..." : string, maybe – Dongdonga

Can also use the elipsis character (…) instead of three .s to save 2 more chars so you can retain as much info as possible – Orlosky

Answer 2

This is how Ruby on Rails does it in their String#truncate method as a monkey-patch:

class String
  def truncate(truncate_at, options = {})
    return dup unless length > truncate_at

    options[:omission] ||= '...'
    length_with_room_for_omission = truncate_at - options[:omission].length
    stop = if options[:separator]
      rindex(options[:separator], length_with_room_for_omission) || 
        length_with_room_for_omission
      else
        length_with_room_for_omission
      end

    "#{self[0...stop]}#{options[:omission]}"
  end
end

Then you can use it like this

'And they found that many people were sleeping better.'.truncate(25, omission: '... (continued)')
# => "And they f... (continued)"

Nitrogenous

Answer 3

You can write a wrapper around puts that handles truncation for you:

def pleasant(string, length = 32)
  raise 'Pleasant: Length should be greater than 3' unless length > 3

  truncated_string = string.to_s
  if truncated_string.length > length
    truncated_string = truncated_string[0...(length - 3)]
    truncated_string += '...'
  end

  puts truncated_string
  truncated_string
end

Bride

It returns nil which makes it a little harder to test. It should probably just return a truncated string. – Ns

Updated answer to return the truncated string, as @Ns suggested. – Bride

You missed an underscore though: truncated_string – Frasco

Answer 4

You can just use this syntax:

"mystring"[0..MAX_LENGTH]

[5] pry(main)> "hello world"[0..10]
=> "hello world"
[6] pry(main)> "hello world why"[0..10]
=> "hello world"
[7] pry(main)> "hello"[0..10]
=> "hello"

There's no need to check if it actually exceed the maximum length.

Higgs

Answer 5

Truncate naturally

I want to propose a solution that truncates naturally. I fell in love with the String#truncate method offered by Ruby on Rails. It was already mentioned by @Oto Brglez above. Unfortunately I couldn't rewrite it for pure ruby. So I wrote this function.

def truncate(content, max)    
    if content.length > max
        truncated = ""
        collector = ""
        content = content.split(" ")
        content.each do |word|
            word = word + " " 
            collector << word
            truncated << word if collector.length < max
        end
        truncated = truncated.strip.chomp(",").concat("...")
    else
        truncated = content
    end
    return truncated
end

Example

• Test: I am a sample phrase to show the result of this function.
• NOT: I am a sample phrase to show the result of th...
• BUT: I am a sample phrase to show the result of...

Note: I'm open for improvements because I'm convinced that there is a shorter solution possible.

Wilow

Answer 6

You can use the truncate gem for this:

require 'truncate'
long_string = "this is a very long long long long long long long long"
puts long_string.truncate

Rigorous