From: Robert Klemme <shortcutter@...>
Date: 2008-04-27T00:20:07+09:00
Subject: Re: All occurances of a  character in a string

On 26.04.2008 16:53, David A. Black wrote:
> Hi --
> 
> On Sat, 26 Apr 2008, Raghu Go wrote:
> 
>> Hi - I am trying to figure out the ruby way of printing all occurances
>> of a character in a string..
>>
>> The index method on string gives only the first occurance only.
>>
>> Example input string - abbccdaab
>> desired output - 'a' = 0 6 7
>>                 'b' = 1 2 8
>>                 'c' = 3 4
>>                 'd' = 5
>>
>> Any help greatly appreciated..
> 
> I have this really strong feeling that there's a really easy way, but
> I can't think of it or find it. Meanwhile, if you're using 1.9 you
> could do something like:
> 
>    str = "abcdbcdae"
> 
>    h = Hash.new {|h,k| h[k] = [] }
>    str.each_char.map.with_index {|char, i| h[char] << i }
> 
> which would put a hash of results in h.

In 1.8

irb(main):001:0> require 'enumerator'
=> true
irb(main):002:0> str = "abcdbcdae"
=> "abcdbcdae"
irb(main):003:0> ind = Hash.new {|h,k| h[k]=[]}
=> {}
irb(main):004:0> str.to_enum(:scan,/./).each_with_index {|c,i|ind[c]<<i}
=> #<Enumerable::Enumerator:0x7ff75768>
irb(main):005:0> ind
=> {"a"=>[0, 7], "b"=>[1, 4], "c"=>[2, 5], "d"=>[3, 6], "e"=>[8]}

> I just have this hunch that there was a way to accumulate offsets from
> a scan or gsub operation, but I can't come up with it.

Like this?

irb(main):017:0> str = "abcdbcdae"
=> "abcdbcdae"
irb(main):018:0> ind = Hash.new {|h,k| h[k]=[]}
=> {}
irb(main):019:0> str.scan(/./) {|c| ind[c] << $`.length}
=> "abcdbcdae"
irb(main):020:0> ind
=> {"a"=>[0, 7], "b"=>[1, 4], "c"=>[2, 5], "d"=>[3, 6], "e"=>[8]}

Cheers

	robert