Ruby - 将所有字符切片直到字符串中的下划线

Question

I have a string like this solution_10 and I would like to remove the part solution_ from it, the number after the underscore will increase, it can be 100 , 1000 and even larger. I cant seem to wrap my head around on how to do this.

I have tried to use slice!(0, 9) but that gives me solution_ , I then tried slice!(0, -2) but that gives me null,

I then tried using solution_10[1..9] this gives me ortable_1

So my question is how to get rid of all characters till underscore , all I want is the number after the underscore.

Answer 1

Use String#split method

'solution_10'.split('_').last #will return original string if no underscore present
#=> "10"

'solution_10'.split('_')[1] #will return nil if no underscore present
#=> "10"

Answer 2

"solution_10"[/(?<=_).*/]
#⇒ "10"

or simply just get digits until the end of the line:

"solution_10"[/\d+\z/]
#⇒ "10"

Answer 3

Another way:

'solution_10'[/\d+/]
#=> "10"

Answer 4

I cant seem to wrap my head around on how to do this.

First of all, slice and its shortcut [] can be used in many ways. One way is by providing a start index and a length :

'hello'[2, 3] #=> "llo" # 3 characters, starting at index 2
#  ^^^

You can use that variant if you know the length in advance. But since the number part in your string could be 10 or 100 or 1000 , you don't.

Another way is to provide a range, denoting the start and end index:

'hello'[2..3] #=> "ll"  # substring from index 2 to index 3
#  ^^

In this variant, Ruby will determine the length for you. You can also provide negative indices to count from the end. -1 is the last character, -2 the second to last and so on.

So my question is how to get rid of all characters till underscore, all I want is the number after the underscore.

We have to get the index of the underscore:

s = "solution_10"
i = s.index('_') #=> 8

Now we can get the substring from that index to the last character via:

s[i..-1] #=> "_10"

Apparently, we're off by one, so let's add 1:

s[i+1..-1] #=> "10"

There you go.

---

Note that this approach will not necessarily return a number (or numeric string), it will simply return everything after the first underscore:

s = 'foo_bar'
i = s.index('_') #=> 3
s[i+1..-1]       #=> "bar"

It will also fail miserably if the string does not contain an underscore, because i would be nil :

s = 'foo'
i = s.index('_') #=> nil
s[i+1..-1]       #=> NoMethodError: undefined method `+' for nil:NilClass

For a more robust solution, you can pass a regular expression to slice / [] as already shown in the other answers. Here's a version that matches an underscored followed by a number at the end of the string. The number part is captured and returned:

"solution_10"[/_(\d+)\z/, 1] #=> "10"
#              _          literal underscore
#               (   )     capture group (the `1` argument refers to this)
#                \d+      one or more digits
#                    \z   end of string

Answer 5

Why don't just make use of regex

"solution_10".scan(/\d+/).last
#=> "10"