Prepend a character to a string in ruby

Ruby
1

Hi,

I am trying to insert a character to a string at the beginning of a
string. How is it possible in ruby.
I tried using
s.times do |s|
@space_availability+=“0”
end
But this would add at the end of the string.
The @space_availability is a string with 1’s and 0’s. I need to add 0’s
at the beginning of this string.
I am a newbie in ruby

2

On Wednesday 31 August 2011 20:00:40 ruby rails wrote:

at the beginning of this string.
I am a newbie in ruby

@space_availlability.insert 0, “0”

You can find documentation for a class or method using the ri command
line
tool:

ri String

or

ri String#insert

I hope this helps

Stefano

3

Another way:

x = “foobar” # => “foobar”
x[0,0] = "this is prepended " # => "this is prepended "
x # => “this is prepended foobar”

x variable now is “this is prepended foobar” as you can see from IRB
output.

There are many more ways. At least one with a Regex, but it is often
said that Regex has an overhead and hence a speed penalty, thus I think
it is usually better to use a Regex only when needed.

There is also another way in where you re-assemble a string.

x = “foobar”

x = "abcdef " + x

But this would create a new string object.

If you use << then you do not create a new string object. (But this
means append to… sadly there is no prepend to … sometimes I wanted
to use >> to mean prepend…)

4

The other answers are better. I am just posting this for yet another
way to prepend text to a string: String interpolation.

question = "Nancy Francis: Back here live at the Waterfront Village

with my friend
the zombie, Jonathon. You’re looking good, Jonathon. Jonathon just
got an awesome face paint job. What do you think?\n\n"

answer = "Jonathan: I like turtles!"

dialogue = "#{question}#{answer}"
5

On Wed, Aug 31, 2011 at 1:00 PM, ruby rails [email protected]
wrote:

I am trying to insert a character to a string at the beginning of a
string. How is it possible in ruby.
I tried using
s.times do |s|
@space_availability+=“0”
end
But this would add at the end of the string.
The @space_availability is a string with 1’s and 0’s. I need to add 0’s
at the beginning of this string.
I am a newbie in ruby

You can use String#rjust

irb(main):023:0> @space_availability = ‘x’
=> “x”
irb(main):024:0> @space_availability = @space_availability.rjust 5, ‘0’
=> “0000x”

However, chances are that you want printf, sprintf or % operator. For
example

irb(main):013:0> sprintf ‘%0*d’, 10, 8
=> “0000000008”

So, for numbers

@space_availability = sprintf ‘%0*d’, s, int_value

If you want the string to represent a binary number you can do

irb(main):015:0> sprintf ‘%0*b’, 8, 123
=> “01111011”

Note, the ‘’ in the format string indicates there is an argument
indicating the length before the value. If the length is fixed you
can replace '’ with the length:

irb(main):016:0> sprintf ‘%08b’, 8, 123
=> “00001000”

Kind regards

robert

6

On Wed, Aug 31, 2011 at 7:19 AM, Michal S. [email protected]
wrote:

It is sad there is no obvious method for that.

But if it makes you happy, there can be :slight_smile:

ruby-1.8.7-p352 > class String
ruby-1.8.7-p352 ?> def >>(arg)
ruby-1.8.7-p352 ?> self.insert(0, arg)
ruby-1.8.7-p352 ?> end
ruby-1.8.7-p352 ?> end
=> nil
ruby-1.8.7-p352 > string = “bar”
=> “bar”
ruby-1.8.7-p352 > string >> “foo”
=> “foobar”
ruby-1.8.7-p352 >

7

On 31 August 2011 13:44, Marc H. [email protected] wrote:

Another way:

x = “foobar” # => “foobar”
x[0,0] = "this is prepended " # => "this is prepended "
x # => “this is prepended foobar”

x variable now is “this is prepended foobar” as you can see from IRB
output.

This is nice.

It is sad there is no obvious method for that.

Thanks

Michal

8

On Aug 31, 2011, at 08:29 AM, Hassan S.
[email protected] wrote:
On Wed, Aug 31, 2011 at 7:19 AM, Michal S. [email protected]
wrote:

It is sad there is no obvious method for that.

But if it makes you happy, there can be :slight_smile:

ruby-1.8.7-p352 > class String
ruby-1.8.7-p352 ?> def >>(arg)
ruby-1.8.7-p352 ?> self.insert(0, arg)
ruby-1.8.7-p352 ?> end
ruby-1.8.7-p352 ?> end
=> nil
ruby-1.8.7-p352 > string = “bar”
=> “bar”
ruby-1.8.7-p352 > string >> “foo”
=> “foobar”
ruby-1.8.7-p352 >

Since we’re monkeypatching and mutating anyway, I like reversing the
order so that the order of the arguments is the same as in the result:

irb(main):001:0> class String
irb(main):002:1> def >>(other)
irb(main):003:2> other.insert(0,self)
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> str = “bar”
=> “bar”
irb(main):007:0> “foo” >> str
=> “foobar”

9

On Wed, Aug 31, 2011 at 5:00 AM, ruby rails
[email protected]wrote:

at the beginning of this string.
I am a newbie in ruby

It is coming:

String#prepend has been accepted as revision r29120.

10

On Wed, Aug 31, 2011 at 4:46 PM, Gavin K. [email protected] wrote:

ruby-1.8.7-p352 > class String

=> “bar”
irb(main):007:0> “foo” >> str
=> “foobar”

That triggered another idea:

irb(main):001:0> class String
irb(main):002:1> def head=(s)
irb(main):003:2> insert 0, s
irb(main):004:2> end
irb(main):005:1> def tail=(s)
irb(main):006:2> self << s
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):009:0> s = “foo”
=> “foo”
irb(main):010:0> s.head = “begin(”
=> “begin(”
irb(main):011:0> s
=> “begin(foo”
irb(main):012:0> s.tail = “)end”
=> “)end”
irb(main):013:0> s
=> “begin(foo)end”

Note the absence of readers. Reasoning about why left as exercise for
the reader. :slight_smile:

Kind regards

robert